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THE    ANATOMY 


HUMAN  PERITONEUM 

AND 

ABDOMINAL  CAVITY 


CONSIDERED  FROM  THE  STANDPOINT  OF  DEVELOPMENT 
AND  COMPARATIVE  ANATOMY 


BY 


GEORGE  S.  gUNTINGTON,  M.A.,  M.D. 

PROFBSSOR  OF  ANATOMY,  COLLEGE  OF  PHYSICIANS  AND  SURGEONS,  COLOMBIA  UNIVERSITY, 

NEW   YORK   CITY 


ILLUSTRATED  WITH  300  FULL-PAGE  PLATES  CONTAINING 
682   FIGURES,  MANY  IN  COLORS 


LEA  BROTHERS  &  CO. 

PHILADELPHIA    AND    NEW   YORK 
1903 


Entered  according  to  the  Act  of  Congress,  in  the  year  1903,  by 

LEA    BROTHERS    &    CO., 
In  the  Office  of  the  Librarian  of  Congress.     All  rights  reserved 


\  903. 


PREFACE. 


In  the  following  pages  an  attempt  has  been  made  to  empha- 
size the  value  of  Embryology  and  Comparative  Anatomy  in 
elucidating  the  difficult  and  often  complicated  morphological 
problems  encountered  in  the  study  of  human  adult  anatomy. 

Moreover,  in  addition  to  the  direct  advance  in  the  method  and 
scope  of  anatomical  teaching  afforded  by  these  aids,  it  is  further 
hoped  that  the  broader  interpretation,  both  of  structure  and  func- 
tion, obtained  by  ontogenetic  and  phylogenetic  comparison,  will 
impart  an  interest  to  the  study  of  adult  human  morphology,  such 
as  the  subject,  considered  solely  in  the  narrow  field  of  its  own 
limitations,  could  never  arouse. 

The  book  represents  part  of  the  course  in  visceral  anatomy  as 
developed  during  the  past  fourteen  years  at  Columbia  Univer- 
sity. The  sections  dealing  with  the  morphology  of  the  vertebrate 
ileo-colic  junction  and  with  the  structural  details  of  the  human 
caecum  and  appendix  are  considered  somewhat  more  fully,  as 
warranted  by  the  extensive  material  available.  The  illustra- 
tions are  for  the  greater  part  taken  from  preparations  in  the 
Morphological  Museum  of  the  University.  Wherever  practicable 
the  direct  photographic  reproduction  of  the  actual  preparation  is 
given.  .  In  the  case  of  preparations  not  suitable  for  this  purpose, 
careful  drawings  have  been  made  which  offer  in  every  instance  a 
faithful  and  correct  interpretation  of  the  conditions  presented  by 
the  actual  object.  A  number  of  the  embryonic  illustrations  are 
taken  from  the  standard  text- books  on  the  subject,  due  credit 
being  given  to  their  source.  I  desire  to  express  my  sincere 
thanks  to  Dr.  Edward  Leaming,  of  the  Department  of  Photog- 
raphy and  to  Mr.  M.  Petersen,  artist  of  the  Anatomical  Depart- 
ment of  the  University,  for  their  skilful  and  thoroughly  reliable 
work  in  the  preparation  of  the  illustrations. 

George  S.  Huntington. 

Columbia  Univkesity,  in  the  City  of  New  York, 
December,  190S. 


3424 


CONTENTS. 


Page, 

Introduction.         .        .        . 17 

Development  of  Vertebrate  Ovum     ........  19 

Development  of  Ccelom  and  of  Alimentary  Canal 21 

Development  of  Cloaca 24 

Development  and  Divisions  of  the  Peritoneum 82 

Derivatives  of  Entodermal  Intestinal  Canal 34 

Divisions  of  Alimentary  Canal 38 

Part  I.     Anatomy  of  the  Peritoneum  and  Abdominal  Cavity         .        .  39 

Comparative  Anatomy  of  Foregut  and  Stomach         .        ...  42 

Morphological  Types  of  Stomach 43 

Development  of  the  Intestine 51 

I.  Intestinal  Rotation  and  Definition  of  Adult  Segments  of  the  Intes- 

tinal Canal 58 

Development  of  Aortal  Arterial  System 63 

II.  Demonstration  of  Intestinal  Rotation  in  the  Lower  Mammalia      .     67 

Peritoneal  and  Visceral  Relations  in  the  Infracolic  Compartment 

of  the  Abdominal  Cavity  in  the  Adult 74 

Part  II.     Anatomy  of  the  Peritoneum  in  the  Supracolic  Compart- 
ment OF  the  Abdomen 99 

1.  Stomach  and  Dorsal  Mesogastrium 100 

a.  Changes  in  Position  of  Stomach •    .         .   102 

b.  Changes  in  Direction  and  Extent  of  Dorsal  Mesogastrium       .         .  103 

c.  Development  of  Spleen  and  Pancreas  in  the  Dorsal  Mesogastrium 

and  Changes  in  the  Disposition  of  the  Great  Omentum      .         .108 

1.  Development  of  Spleen     ........  108 

.  Ill 

.  115 

.  116 

.  119 

.  122 


2.  Development  of  Pancreas         .... 

Development  of  Pancreas  in  Lower  Vertebrates 

Comparative  Anatomy  of  Pancreas  . 

Pyloric  Cseca  or  Appendices     .... 

Peritoneal  Relations  of  Pancreas 

Comparison  of  Embryonal  Stages  during  the  Development  of 
the  Human  Dorsal  Mesogastrium,  Spleen  and  Pancreas  with 
the  Permanent  Adult  Condition  of  the  same  Structures  in 
Lower  Mammalia  ........  126 


1.  Spleen,  Pancreas  and  Great  Omentum  of  Cat  . 

2.  Relation  of  Great  Omentum  to  Transverse  Colon,  Transverse 

Mesocolon  and  Third  Part  of  Duodenum 

Ventral  Mesogastrium  and  Liver 

I.  A.  Development  of  Liver 

B.  Comparative  Anatomy  of  Liver.         .         .         .         .         . 

C.  Development  of  Vascular  System  of  Liver 

Comparative  Anatomy  of  the  Hepatic  Venous  Circulation 


127 

129 
140 
141 
144 
145 
154 


Vi  CONTENTS. 

Page. 

II.  Ventral  Mesogastrium 163 

Peritoneal  Relations  of  Liver 167 

Eelation  of  Hepatic  Peritoneum  to  the  "  Lesser  Sac  "  .         .         .  174 

Caudal  Boundary  of  Foramen  of  Winslow 178 

Pancreatico-gastric  Folds 181 

Part  HI.   Large  and  Small  Intestine,  Ileo-colic  Junction  and  C^cum.  189 

I.  General  Review  of  Morphology  and  Physiology  of  the  Verte- 

brate Intestine 190 

I.  Midgut  or  Small  Intestine 192 

Intestinal  Folds .193 

Divisions  of  Small  Intestine 194 

Structure  of  Small  Intestine 194 

1.  Secretory  Apparatus  .         .         .         .         .         .         .194 

2.  Absorbing  Apparatus 195 

Valvules  Conniventes •         .  196 

II.  Endgut  or  Large  Intestine 198 

II.  Serial  Review  of  the    Ileo-Colic    Junction   and    Connected 

Structures  in  Vertebrates 200 

I.  Fishes 200 

II.  Amphibia 201 

III.  Reptilia 201 

IV.  Birds 203 

V.  Mammalia 204 

Monotremata 204 

Marsupalia 204 

Edentata 206 

Sirenia 208 

Cetacea •       .         .         .         .  209 

Ungulata 209 

Rodentia 211 

Carnivora       ..........  212 

Cheiroptera  .         .         ........  212 

Insectivora 213 

Primates        ..........  213 

III.  Phylogbny  of  the  Types   of  Ileo-colic  Junction  and  Cjecum  in 
the  Vertebrate  Series 217 

1.  Symmetrical  Form  of  Ileo-colic  Juncton  ;  Mid-  and  End-gut 

in  Direct  Linear  Continuity .221 

2.  Asymmetrical  Development  of  a  Single  Caecal  Pouch,  lateral 

to  the  Ileo-colic  Junction,  Mid-  and  End-gut  Preserving  their 
Linear  Continuity  ........   223 

3.  Rectangular  Ileo-colic  Junction,  with  Direct  Linear  Continuity 

of  Caecum  and  Colon 225 

Structure  of  C^cal  Apparatus  and  Specialized  Morphological 

Characters  of  Colon  in  Rodents  and  Ungulates     .        .        .  229 

1.  Caecum  Proper         ..........  229 

2.  Structural  Modifications  of  Proximal  Segment  of  Colon  analogous 

in  their  Functional  Significance  to  the  Csecal  Apparatus  .         .         .  230 

Part  IV.   Morphology  of  the  Human  C^cum  and  Vermiform  Appendix.  237 

I.  Development  of  the  Csecum  and  Appendix 237 


CONTENTS.  VU 

Page. 
II.  Changes  in  the  Position  of  the  Caecum  and  Appendix  during  normal 
Development,  depending  upon  the  Rotation  of  the  Intestine  and 
the  subsequent  Descent  of  the  Caecum     ......  239 

in.  Variations  of  Adult  Caecum  and  Appendix  .....  244 

A.  Shape  of  Caecum  and  Origin  of  Appendix.     Types  and  "Variations 

of  Adult  Caecum  and  Appendix   .......  245 

B.  Position  and  Peritoneal  Relations  of  Appendix      ....  250 
a  Ileo-Csecal  Folds  and  Fossae 260 


PLATE    I. 


ZONA 
PELLUCIDA 


CLEAR    LAYER 


EPITHELIUM 
OF   FOLLICLE 


GERMINAL 
VESICLE 
GERMINAL 
SPOT 


FIBRILLAR 
LAYER 


Fig.  1. — Human  ovum,  from  a  mature  follicle,  a  sphere  of  about 
0.2  mm.  diameter.     X  25.     (KoUmann.) 


THE    SMALLER 
BLASTOMERE 


ZONA 
PELLUCIDA 


THE    LARGER 
BLASTOMERE 


Fig.  2. — Segmentation  of  mammalian  ovum  (bat).  (After  E.  von 
Beneden.)  Two  blastomeres,  each  with  a  nucleus,  shown  in  lighter 
color.     The  dark  bodies  are  yolk-granules. 


Fig.  3. — Segmentation  of  mammalian  ovum.  Fig.  4. — Ovum  of  rabbit,  from  terminal  por- 

Four  Vjlastomeres.     (After  E.  von  Beneden.)  tion  of   oviduct.      The   zona   pellucida  appears 

thickened,  and  contains  many  spermatozoa  which 
failed  to  penetrate  the  ovum.     (After  Bischofl".)  f 


PLATE    II. 


ALBUMINOUS 
ENVELOPE 


GERMINAL 
MEMBRANE 
OR    BLASTODERM 


ZONA 
PELLUCIDA 


GERMINAL 
AREA 


CAVITY    OF 
BLASTOSPHERC 


Fig.  5. — Blastodermic  vesicle  of  rabbit.     (After  E.  von  Beneden.) 


SEGMENTATION    CAVITY 


MARGINAL   ZONE    OF 
GERMINAL    MEMBRANE 


INNER    CELL-MASS    FORMING 
GERMINAL   AREA 


Fig.  6. — Blastodermic  vesicle  of  Triton  tseniatus.    (Hertwig.) 


PRIMITIVE 
STREAK 


HEAD    PROCESS 


NEURENTERIC 
CANAL 


Fig.  7. — Embryonic  ana  of  rabbit  embryo.  (Heis- 
ler,  after  E.  von  Beuedeu.)  The  primitive  streak  begin- 
ning m  the  cell-proliferation  known  as  the  "node  of 
Hensen." 


RAUBCR'S 

PROCHORION 

OR    COVER-LAYER 


ZONA 
FCLUJCJOA 


Fig.  8. — Blastodermic  vesicle  of  mammal.  (E.  von  Bene- 
den.)  The  layer  of  cells  lining  the  interior  of  the  vesicle  next 
to  the  zona  pellucida  forms  Rauber's  "  Deckschichte "  or  pro- 
chorion.  This  is  not  the  true  ectoderm,  since  it  does  not  par- 
ticipate in  the  formation  of  the  embryo,  which  is  entirely 
derived  from  the  cells  of  the  germinal  area. 


ATTACHMENT  OF  AMNION 
AND  CHORION  DRAWN 
OUT  TO    A   TIP 

ALLANTOIC  STALK 
CAUDAL  END 
OF    EMBRYO 


PRIMITIVE    SEGMENT. 


VITELLINE 
BLOOD-VESSELS 


YOLK-SAC 


VISCERAL  ARCHES 


Fig.  9. — Human  embryo  with  yolk-sac,  amnion,  and  belly-stalk 
of  fifteen  to  eighteen  days.     (Heisler,  after  Coste.) 


Fig.  1 0. — Embryonal  area  of  sheep,  composed  of  ectoderm  and  ento- 
derm.    (After  Bonnet.) 


ECTODERM 

MESODERM 
ENTODERM 


Fig.  11. — Blastodermic  vesicle  of  rabbit.     Section  through  embry- 
onic area  at  caudal  limit  of  node  of  Hensen.     (Rabl. ) 


i 


PLATE    IV. 


WALL  OF 

BLASTODERNirC 

VESICLE 


AREA 
PELLUCIDA 


EMBRYONAL 
SHIELD 


Fig.  12. — Oval  oinbiyDiiic  area  of  rabbit's  egg,  detached  with 
part  of  wall  of  blastodermic  vesicle.     X  30.     (Kollmann.) 


PARIETAL   LAYER 
OF   MESODERM 


ECTODERM 


PRIMITIVE    GROOVE 


MESODERM 


BEGINNING    OF 
AMNIOTIC   FOLD 


PRIMITIVE    CCZLOM 


VISCERAL    LAYER 
OF   MESODERM 


PRIMITIVE    STREAK 


ENTODERMAL    LINING    OF 
ENTODERM  INTESTINAL    FURROW 


Fig.  13.— Transverse  section  of  embryonic  area  of  ovum  of  sheep  of  fourteen  and  a  half 
days.    (Heisler,  after  Bonnet.) 


WALL  OF 

BLASTODERMIC 

VESICLE 


TERMINAL 
KNOB 


AREA    OF 

MEDULLARY 

FOLDS 


PRIMITIVE 
FURROW 


Fig.  14. — Germinal  luva  i>l   rabbit's  ovum.     (Kollmann.) 


PLATE   V. 


MEDULLARY 
FOLOS 


I 

I 


MEDULLARY 
GROOVE 


PRIMITIVE 

STREAK    AND 

GROOVE 


Fig.  15. — Surface-view  of  area  pellucida  of  an 
eighteen-hour  chick -embryo.     (Balfour.) 


MEDULLARY 


AMNIOTIC 
MESODERM 


AMNIOTIC 
ECTODERM 


YOLK-SAC 
MESODERM 


ECTODERM 


MESODri:RM 


MESOUERMAL. 
CLEFT 


ENTODERM 


Fig.  16. — Transverse   section  of  human    embryo  before  develop- 
ment of  protovertebrae  or  chorda  dorsalis.     (Keibel.) 


i 


AMNION 

MEDULLARY    FURROW 


MESODERM 


PARIETAL 
MESODERM 


VISCERAL 
MESODERM 


PLEURO-PERICARDIAL 
CAVITY 


ENTODCRMAL    LINING    OF 
HEART        \  PRIMITIVE    HEAD-GUT 

PLATE         PRIMITIVE    ENDOCARDIUM 


EXTENSION    OF 
CCELOM 


Fig.  17. — Transverse  section  of  a  sixteen  and  a  half  day  sheep  embryo.  (Heisler,  after  Bonnet. 


PLATE   VI. 


mi;dullary  tube 


PROTOVERTEBR* 


WOLFFIAN    DUCT 


PARIETAL    MESODERM 
UNITING    WITH    ECTO- 
DERM    TO     FORM 
SOMATOPLEURE 


ENTODERM 


PARAXIAL   MESODERM 


VISCERAL    MESODERM 
UNITING    WITH    ENTO- 
DERM   TO     FORM 
SPLANCHNOPLEURE 


Fig.  18. — Embryo  of  bird,  at  begiiniiug  of  third  day,  with  four  blasto- 
dermic layers,  resulting  from  the  division  of  the  mesoderm  into  parietal 
and  visceral  layers,  separated  by  the  ccelom  cavity.  Transverse  section, 
X  170.     (Kollmann.) 


SOMITE    OR 
LATERAL       PROTOVERTEBRA 
ZONE 


AXIAL 
ZONE 


MEDULLARY 
TUBE 


CAVITY    WITHIN 
SOMITE 


ECTODERM 


LATERAL   PLATES 
FOR   BODY-WALL 


LATERAL    PLATES    FOR 
INTESTINAL  CANAL 


PARIETAL  MESODERM 
FUSED  WITH  ECTO- 
DERM 


PLEURO- PERITONEAL 
CAVITY 

VISCERAL    MESODERM 
UNITED    TO     ENTO- 
DERM 


-VITELLINE    VEIN 


INTESTINAL 
ENTODERM 


PRIMITIVE 
AORTiE 


Fig.  19.— Transverse  section  of  a  seventeen  and  a  half  day  sheep  embryo.    (Bonnet.) 


PLATE   VII. 


MEDULLARY 
PLATES 


PARIETAL. 
MESODERM 


VISCERAL 
MESODERM 


ENTODERM 


MEDULLARY 
GROOVE 


INTESTINAL 
TUBE 


YOLK-SAC 


Fig.  20. — Curves  of  blastodermic  layers  and  division 
of  mesoderm  in  amniote  embryo.     (KoUmaun.) 


CLOACA 
CLOACAL   MEMBRANE. 

PROCTODCEAL 
INVAGINATION 
OF   ECTODERM 


:ntestine 


CANAL  OF 
ALLANTOIS 


CAUDAL  END 
OF   EMBRYO 

POST-ANAL   GUT 
CHORDA    DORSALIS 
MEDULLARY   CANAL 


Fig.  21. — Sagittal  section  of  caudal  extremity  of  cat  embryo  of  6  mm. 
(Tourneux.) 


ECTODERM 


MEDULLARY 
FOLDS 


PRIMITIVE 
FURROW 


CLEFT   OF 

MESODERM 

MEDULLARY 

GROOVE 


NEURO-ENTERIC 
CANAL 


PRIMITIVE 
RIDGES 


ALLANTOIC 
STALK 


Fig.  22. — Caudal  half  of  human  blastoderm  measuring  3  mm., 
with  open  medullarj-  groove.     Dorsal  view.     X  30.     (After  Spee.) 


PLATE   VIII. 


PROBE    IN    ABDOM- 
INAL  OPENING    OF 
RIGHT   OVIDUCT 


CUT  EDGE  OF  RIGHT 
MESOVARIUIM 


INTESTINE 


CLOACAL   ORIFICE 

OF    BLADDER 

CLOACAL   ORIFICES 

OF   OVIDUCTS 


LEFT   OVARY 


URINARY    PAPILLA 

WITH     PROBES    IN 

URETERAL   0R:FICES 


Fig.  23.— Goiiito-urinary  tract  and  cloaca  of /(/((rtim  ^Hfte/'CK^rt^rt,    9.     (Columbia  University 

Museum,  No.  1846.) 


INTRODUCTION. 


In  considering  the  anatomy  of  the  human  abdominal  cavity 
and  peritoneum  in  the  following  pages  the  explanation  of  the 
adult  conditions  encountered  is  based  upon  the  development  of 
the  parts,  and  the  successive  human  embryonal  stages  are  illus- 
trated by  the  examination  of  the  lower  vertebrates  presenting 
permanent  adult  structural  conditions  which  appear  as  merely 
temporary  embryonal  stages  in  the  development  of  the  higher 
mammaUan  ahmentary  tract. 

For  the  sake  of  clearness  and  brevity  all  discussion  of  the  theories! 
of  peritoneal  development  has  been  designedly  omitted.  The  as- 
sumption of  peritoneal  adhesion,  and  consequent  obliteration  of 
serous  areas,  offers  many  advantages  in  considering  the  adult 
human  abdominal  cavity,  especially  from  the  standpoint  of  com- 
parative anatomy.  The  same  has  consequently  been  adopted 
without  reference  to  divergent  views  and  theories. 

In  studying  the  descriptive  text  and  the  diagrams  the  student 
should  remember  that  the  volume  offers  in  no  sense  a  complete 
or  detailed  account  of  the  development  of  the  abdominal  cavity 
and  its  contents.  The  purpose  is  not  to  present  the  embryology 
of  this  portion  of  the  vertebrate  body,  but  to  utilize  certain  embry- 
ological  facts  in  order  to  explain  the  complicated  adult  conditions 
encountered.  To  avoid  confusion,  and  to  bring  the  salient  points 
into  strong  relief,  the  majority  of  the  diagrams  illustrating  human 
embryonal  stages  are  purely  schematic. 

Moreover,  in  order  to  avoid  confusing  and  unnecessary  details 
it  is  often  desirable  to  disregard  developmental  chronology  en- 
tirely. Many  of  the  diagrams  combine  several  successive  devel- 
opmental stages,  showing  different  degrees  of  development  in 
different  portions  of  the  same  drawing.  Again  it  is  frequently 
2  17 


18     *  ABDOMINAL  CAVITY  AND  PERITONEUM. 

necessary,  for  the  sake  of  brevity  and  clearness,  to  actually  depart 
from  known  embryological  conditions.  If,  for  example,  the  stom- 
ach and  liver  are  treated  as  if  they  were  from  their  inception 
abdominal  organs,  the  student  of  systematic  embryology  will  recall 
the  fact  that  this  position  is  only  obtained  after  their  primitive 
differentiation  by  growth  and  migration. 

Again  the  mesenteries  are  treated  here  as  if  they  formed  definite 
and  well-defined  membranes  from  the  beginning — without  refer- 
ence to  the  abdominal  organs  with  which  they  are  associated.  We 
speak  of  the  liver  as  growing  into  and  between  the  layers  of  the 
ventral  mesogastrium,  because  this  conception  offers  the  oppor- 
tunity of  more  clearly  explaining  the  adult  condition.  Actually, 
however,  the  membrane  develops,  as  a  new  structure,  after  the 
first  differentiation  of  liver  and  stomach,  as  these  organs  descend 
into  the  abdominal  cavity. 

Similar  discrepancies  between  fact  and  schema  are  encountered 
throughout.  Consequently,  while  the  purpose  of  the  volume  is  to 
facilitate  the  study  and  comprehension  of  the  adult  peritoneal 
cavity  and  its  contents,  the  reader  should  guard  against  receiving 
the  developniental  illustration  as  a  correct  successive  and  detailed 
account  of  the  embryology  of  the  parts  concerned. 

In  like  manner  the  comparative  anatomical  facts  adduced  form 
in  no  sense  even  approximately  a  complete  serial  morphological 
account  of  the  vertebrate  alimentary  tract. 

To  the  student  of  human  anatomy  the  zoological  position  of  the 
forms  which  help  him  to  understand  complicated  human  struc- 
tural conditions  is  immaterial.  He  can  draw  on  all  the  verte- 
brate classes  independently  of  their  mutual  relations.  Hence 
neither  ontogeny  nor  phylogeny  are  here  introduced,  except  as 
aids  to  the  study  of  adult  human  anatomy.  The  following  pages 
offer  neither  an  embryology  nor  a  comparative  anatomy  of  the 
alimentary  tract,  but  an  attempt  has  been  made  in  them  to  illus- 
trate the  significance  of  the  complicated  anatomical  details  pre- 
sented by  the  adult  human  abdominal  cavity  by  reference  to  the 
simpler  antecedent  conditions  encountered  during  the  early  de- 


INTRODUCTION.  19 

velopmental  stages  of  the  higher  forms  and  permanently  in  the 
structure  of  the  lower  vertebrates. 

While,  as  just  stated,  a  complete  presentation  of  the  develop- 
ment of  the  abdominal  cavity  is  not  required,  yet  the  student 
will  find  it  of  advantage  to  rehearse  the  main  facts  of  vertebrate 
embryology,  for  the  purpose  of  bringing  a  clear  understanding  of 
the  manner  in  which  the  vertebrate  body  is  built  up  to  bear  upon 
the  problems  which  the  special  organs  and  structures  of  the  body- 
cavity  present  for  his  consideration.  This  purpose  can  be  accom- 
plished by  a  very  brief  and  condensed  consideration  of  the  car- 
dinal facts. 

The  entire  vertebrate  body  is  the  product  of  developmental 
changes  taking  place  after  fertilization  in  a  single  primitive  cell, 
the  EGG  or  OVUM  (Fig.  1). 

In  structure  the  ovum  corresponds  to  other  animal  cells.  On 
account  of  their  special  significance  during  development  the  dif- 
ferent component  parts  of  the  egg-cell  have  received  special  dis- 
tinctive names.  The  cell-body  is  known  as  the  vitellus  or  yolk. 
It  is  composed  of  two  substances,  the  protoplasm  or  formative  yolk 
and  the  deuteroplasm  or  nutritive  yolk,  which  vary  in  their  rela- 
tive proportions  in  the  ova  of  different  animals. 

The  protoplasm  represents  the  material  from  which  in  the 
course  of  development  the  cells  forming  the  body  of  the  indi- 
vidual are  derived,  while  the  deuteroplasm  serves  for  the  nutri- 
tion of  the  ovum  during  the  earHest  stages  of  development. 

The  nucleus  of  the  egg-cell  is  distinguished  as  the  germinal  ves- 
icle, and  its  nucleolus  as  the  germinal  spot. 

The  cell-body  or  vitellus  is  surrounded  by  a  condensed  portion  of 
the  cell  contents  to  which  the  name  of  the  vitelline  membrane  has 
been  applied,  which  in  turn  is  enclosed  by  a  transparent  and  elastic 
cover,  the  zona  pelludda,  presenting  a  radially  striated  appearance. 

The  ovum  is  contained  in  the  cortical  portion  of  the  ovary,  en- 
closed in  the  Graafian  follicle,  a  vesicle  4-8  mm.  in  diameter, 
whose  fibrous  walls  are  lined  by  several  layers  of  epithelial  cells, 
which  surround  the  ovum,  forming  the  discus  proligerus. 


20  ABDOMINAL   CAVITY  AND  PERITONEUM. 

After  impregnation  the  egg-cell,  by  a  process  of  repeated  division 
or  cleavage,  undergoes  segmentation,  the  cell-body  being  divided 
successively  into  two,  four,  eight,  sixteen,  thirty-two,  etc.,  cells, 
called  blastomeres  (Figs.  2  and  3).  The  mass  of  cells  finally  re- 
sulting from  this  process  of  segmentation  forms  the  ground  work 
of  the  future  body.  A  vertebrate  ovum  in  this  stage  of  com- 
plete segmentation  is  called  the  morula  from  its  resemblance  to 
a  mulberry  (Fig.  4). 

After  segmentation  is  completed  a  cavity  filled  with  fluid  and 
surrounded  by  the  developing  cells  is  gradually  formed  in  the 
interior  of  the  mass.  This  cavity  is  known  as  the  segmentation- 
cavity.  The  egg  is  now  called  the  blastula,  blastosphere  or  blasto- 
dermic vesicle  and  the  cellular  membrane  enclosing  the  segmenta- 
tion-cavity forms  the  germinal  membrane  or  blastoderm  (Figs.  5 
and  6).  The  cells  of  the  blastoderm  become  aggregated  at  one 
point  on  the  circumference  of  the  vesicle  (dorsal  pole  of  blasto- 
sphere) forming,  when  viewed  from  above,  a  thickened  biscuit  or 
disk-shaped  opaque  area.  This  is  known  as  the  germinal  area, 
or  primitive  blastoderm  or  embryonic  shield  (Figs.  7  and  12). 

This  is  the  first  indication  of  the  coming  division  of  the  entire 
egg-cell  into  the  embryo  proper  and  the  vitelline  or  yolk-sac 
(Figs.  8  and  9).  The  entire  future  individual  develops  from 
the  cells  of  the  germinal  area.  This  area  comprises  both  the 
embryo  proper  and  the  region  immediately  surrounding  it. 

The  remainder  of  the  ovum,  serving  temporary  purposes  of 
nutrition  and  respiration,  gradually  becomes  absorbed  and  dis- 
appears. 

Transverse  sections  at  right  angles  to  the  long  axis  of  the  em- 
br3'onic  area  show  that  the  single  layer  of  cells  composing  the 
primitive  germinal  membrane  becomes  differentiated  first  into 
two  (Fig.  10)  and  subsequently  into  three  layers  of  cells  (Fig. 
11).  At  the  margins  of  the  germinal  area  these  layers  are  of 
course  continuous  with  the  rest  of  yolk-sac  wall.  From  their 
position  in  reference  to  the  center  of  the  cell  the  three  layers  of 
the  blastoderm  are  described  as — 


INTRODUCTION.  21 

1.  The  outer,  Epiblast  or  Ectoderm. 

2.  The  middle,  Mesoblast  or  Mesoderm. 

3.  The  inner,  Hypoblast  or  Entoderm. 

The  central  nervous  system  (brain  and  spinal  cord)  is  derived 
from  the  ectoderm  by  the  development  of  a  groove  in  the  long 
axis  of  the  embryonic  area  (Figs.  13,  14,  16  and  17),  and  by  the 
subsequent  union  in  the  dorsal  midline  of  the  ridges  bounding 
the  groove  to  form  a  closed  tube  (Fig.  18).  (Medullary  groove, 
plates  and  canal.) 

The  following  changes  in  the  ventral  aspect  lead  to  the  forma- 
tion of  the  alimentary  canal  and  body-cavity : 

The  developing  embryo  at  first  lies  flat  on  the  subjacent  yolk- 
mass,  and  subsequently  becomes  gradually  separated  more  and 
more  from  the  rest  of  the  blastoderm  by  grooves  or  furrows  which 
develop  along  the  sides  and  at  the  cephalic  and  caudal  extremity 
of  the  embryo.  The  folds  resulting  from  these  furrows  indent 
the  yolk  more  and  more  as  development  proceeds  and  tend  to 
approach  each  other  at  a  central  point,  the  future  umbilicus. 

In  the  meanwhile  changes  in  the  region  of  the  mesoderm  have 
led  to  conditions  which  produce  a  differentiation  of  the  ventral 
portion  of  the  embryo  into  two  tubes  or  cylinders,  the  alimentary 
or  intestinal  canal  and  the  general  body-cavity,  the  former  being 
included  within  the  latter. 

Early  in  the  course  of  development  a  number  of  spaces  appear 
in  the  mesoderm  on  each  side  of  the  axial  line  of  the  embryo. 
These  spaces  soon  unite  to  form  two  large  cavities,  one  on  each 
side.  Taken  together  these  cavities  constitute  the  coelom  or 
body-cavity,  which  becomes  subdivided  in  the  adult  mammal  into 
the  pleural,  pericardial  and  abdominal  cavities. 

As  these  coelom  cavities  develop  in  the  mesoderm  the  cells  lin- 
ing them  become  distinctly  epithelial.  This  mesodermic  epithe- 
lium lining  the  coelom  is  called  the  mesothelium. 

The  development  of  the  coelom  space  divides  the  mesoderm  on 
each  side  into  an  outer  leaf,  the  somatic  or  parietal  mesoderm,  and 
an  inner  leaf,  the  splanchnic  or  visceral  mesoderm  (Figs.  18  and 


22  ABDOMINAL  CAVITY  AND  PERITONEUM. 

19).  The  former  is  closely  applied  to  the  ectoderm,  forming 
with  it  the  somatopleure  or  hody-wall.  The  latter,  in  close  con- 
tact with  the  entoderm,  forms  with  it  the  splanchnopleure  or  wall 
of  the  alimentary  canal.  In  the  dorsal  median  line  both  somatic 
and  splanchnic  mesoderm  become  continuous  with  each  other 
and  with  the  axial  mesoderm  (Fig.  20). 

The  folds  of  the  splanchnopleure,  indenting  the  yolk-sac,  form 
a  gutter  directly  connected  with  the  yolk,  the  primitive  intestinal 
groove  or  furrow,  whose  margins  gradually  approach  each  other 
(Fig.  20).  In  this  way  the  primitive  alimentary  canal  becomes 
separated  from  the  yolk.  At  first  this  separation  is  ill-defined, 
and  the  channel  of  communication  between  the  primitive  in- 
testine and  the  yolk  is  wide  (Figs.  13,  16,  17  and  19).  The 
folding  of  the  splanchnopleure  completes,  at  an  early  period,  the 
dorsal  and  lateral  walls  of  the  embryonic  gut,  but  ventrally, 
toward  the  yolk,  the  tube  is  incomplete  and  widely  open. 

By  union  and  coalescence  of  the  splanchnopleural  folds,  pro- 
ceeding from  the  caudal  and  cephalic  ends  towards  the  center, 
this  primitive  wide  channel  gradually  becomes  narrowed  down, 
until  the  communication  between  the  yolk-sac  and  the  intestine 
is  reduced  to  a  canal,  the  vitello-intestinal  or  omphalo-mesenteric 
duct.  The  intestinal  gutter  is  thus  converted  into  a  closed  tube 
except  at  the  point  of  implantation  of  the  vitelline  duct  during 
the  persistence  of  this  structure.  In  the  meanwhile  the  somato- 
pleural folds  forming  the  body-walls  grow  more  and  more  together 
from  the  sides,  approaching  the  vitello-intestinal  duct.  Finally 
touching  each  other  they  coalesce  to  form  the  ventral  body  wall, 
in  the  same  manner  as  the  splanchopleural  folds  met  and  united 
to  form  the  alimentary  tube. 

At  the  same  time  the  vitello-intestinal  duct  and  the  remnant 
of  the  yolk-sac,  to  which  it  was  attached  ( "  umbilical  vesicle  " ), 
normally  become  obliterated  and  disappear. 

After  the  intestinal  tube  and  the  body  cavity  have  thus  become 
closed  the  embryo  straightens  out  and  the  alimentary  canal  ap- 
pears as  a  nearly  straight  cylindrical  tube  extending  from  the 


INTRODUCTION.  23 

cephalic  to  the  caudal  end  of  the  embryo.  This  primitive  alimen- 
tary tube  at  first  terminates  at  its  cephalic  extremity  in  a  blind 
pouch,  while  at  the  caudal  end  in  the  early  stages  the  intestine  is 
connected  with  the  nerve-tube  by  a  channel  called  the  neuro-enteric 
canal,  forming  in  the  earliest  embryos  a  communication  between 
the  ectoderm  lining  the  bottom  of  the  medullary  groove  and  the 
entoderm  (Figs.  22  and  26).  In  man  this  stage  is  encountered 
very  early,  in  embryos  of  2  mm.  before  the  formation  of  either 
heart  or  provertebrse. 

At  the  point  where  the  canal  develops  the  primitive  groove 
presents  a  thickened  circumvallate  spot,  marking  the  beginning 
perforation  of  the  medullary  plate  from  the  ectoderm  to  the  ento- 
derm. The  canal  exists  only  for  a  short  period  during  the  earliest 
stages  of  embryonal  life.  It  becomes  rapidly  closed,  the  neural 
and  intestinal  tubes  henceforth  remaining  permanently  separated 
from  each  other. 

The  embryonal  caudal  end  of  the  primitive  alimentary  canal  is 
not  the  final  adult  termination  of  the  tube.  When  the  anal  aper- 
ture is  formed  in  a  manner  to  be  presently  detailed,  the  opening 
is  situated  cephalad  of  the  portion  connected  with  the  nerve-tube 
by  the  neuro-enteric  canal.  Hence  this  terminal  portion  of  the 
early  embryonic  aUmentary  canal  is  called  the  ''post-anal  gut" 
(Fig.  21). 

The  post-anal  gut  and  the  neuro-enteric  canal  are  better  de- 
veloped in  the  embryos  of  the  lower  than  in  those  of  the  higher 
vertebrates.  But  in  all  vertebrates  of  the  present  day  both  of 
these  structures  undergo  regressive  changes  and  finally  disappear 
altogether.  They  serve  to  recall  conditions  which  existed  in 
bygone  ages,  and,  while  they  have  a  long  and  significant  phylo- 
genetic  history,  they  have  lost  among  living  vertebrates  all  physi- 
ological importance. 

After  closure  of  the  neuro-enteric  canal  and  obliteration  of  the 
post-anal  gut  the  alimentary  tube  ends,  during  a  short  period, 
both  cephalad  and  caudad  in  a  blind  pouch.  Very  soon,  how- 
ever, the  ectoderm  becomes  invaginated  at  both  extremities  and 


24  ABDOMINAL  CAVITY  AND  PERITONEUM. 

finally  perforates  into  the  lumen  of  the  intestine,  thus  establish- 
ing the  oral  and  anal  communications  with  the  exterior.  The 
anal  ectodermal  invagination  (proctodseum)  (Fig.  21),  is  smaller 
than  the  oral  (stomadseum)  (Fig.  27),  but  the  intestinal  tube 
forms  an  extensive  pouch  in  the  anal  region  which  descends  to 
meet  the  ectodermal  invagination  of  the  proctodseum.  The  de- 
tails of  the  embryonic  processes  leading  to  the  final  establishment 
of  the  adult  condition  are  of  great  interest  on  account  of  the 
pathological  importance  of  abnormal  or  arrested  development  in 
these  parts.  Failure  of  the  caudal  intestinal  pouch  to  establish  a 
communication  with  the  anal  invagination,  or  failure  of  develop- 
ment in  either  anal  invagination  or  intestinal  pouch,  leads  to  the 
condition  known  as  atresia  ani  or  imperforate  anus,  of  which 
there  are  several  varieties. 

Before  the  anal  opening  forms  the  primitive  caudal  intes- 
tine receives  firom  above  the  stalk  of  the  allantois,  while  the 
Wolffian  duct,  the  canal  of  the  embryonic  excretory  appa- 
ratus, also  opens  into  it.  The  renal  bud  on  the  Wolffian  duct  in 
Fig.  28  indicates  the  beginning  development  of  the  permanent 
kidney  (metanephros),  and  the  proximal  portion  of  the  allantoic 
stalk  is  destined  to  form  by  a  spindle-shaped  enlargement  the 
future  urinary  bladder  (Fig.  28).  The  caudal  gut  has  as  yet 
no  anal  opening.  Ventrad  of  the  tail  end  of  the  embryo  the 
ectoderm  presents  at  this  time  a  depression  (Fig.  21).  The 
ectoderm  lining  the  bottom  of  this  anal  fossa  or  depression  is 
separated  by  a  little  mesoderm  tissue  from  the  entodermal  lin- 
ing of  the  blind  pouch  of  the  caudal  gut.  Ectoderm  and  en- 
toderm in  this  region  with  the  intervening  mesodermal  layer 
form  the  cloacal  membrane  (Fig.  21). 

Development  of  Cloaca. — The  entodermal  pouch  or  prolongation 
sent  down  from  the  end-gut  to  meet  the  anal  invagination  en- 
larges and  dilates  to  form  a  short  wide  piece  of  the  intestinal 
tube  into  which  open  on  the  one  hand  the  urinary  and  sexual 
ducts  of  the  genito-urinary  system,  while  it  receives  on  the 
other  the  termination   of  the  end-gut  proper   (Figs.  28  and  29). 


PLATE    IX. 


ENTRANCE    OF    INTESTINE 
INTO    CLOACA 


UPPER    COMPARTMENT   OF 
CLOACA    (cOPROD/EUm) 
OPENINGS    OF    URETERS 
INTO    CENTRAL    COMPART- 
MENT   OF    CLOACA 
(uROD£UM) 

LOWER    COMPARTMENT  OF 

CLOACA  (proctod;eum) 


ABDOMINAL 

OSTIUM  OF 

OVIDUCT 


Fig.  24. — Geuito-urinary  tract  and  cloaca  of  the  hen,   Gallus  bankiva. 
versity  Museum,  No.  1208.) 


CLOACAL   OPENING 

OF   OVIDUCT    INTO 

URODiEUM 


(Columbia  Uni- 


PLATE    X. 


VAS    DEFERENS 


EPIDIDYMIS 


GENITO-UHINARY 
SINUS 


_PENIS    ENVELOPED    IN 
FIBROUS    SHEATH 


CLOACA    FORMED 
CONFLUENCE    OF 
GENITO-URINARY 

SINUS    AND    RECTU 


OPENING    IN    VENTRAL 
—WALL   OF   CLOACA    FOR 
EVERSION    OF    PENIS 


V'V 


<q.    i^um',  25.— Genito-urinary  tract  aud  cloaca  of  Phhjpiis  avatinus, 
duck-billed  platypus.     (Columbia  University  Museum,  No.  1802.) 


ECTODERM 


MESODERM 


ENTODERM 


Fig.  26.— Neuro-enteric  canal  in  section  of  human  embryo  of  2  mm.     (After  Si)ee.) 


PLATE    XI. 


CEREBRAL   VENTRICLE 


SITE    OF   HYPOPHYSIS 

PHARYNGEAL    MEMBRANE 

SEPARATING    STOMAOSUM 

AND    FORE-GUT 


STOMADiEUM 


HEART 
LUMEN    OF   FORE-GUT 


THALAMENCEPHALON 


FOURTH    VENTRICLE 


CENTRAL   CANAL 
SPINAL   CORD 


CHORDA    DORSALIS 


Fig.  27. — Mediau  section  through  head  of  embryo  rabbit  of  6  mm.    (Mihulkovics.) 


DUCT   OF 
ALLANTOIS 


URORECTAL. 
SEPTUM 


CLOACAL 
MEMBRANE 


CAUDAL    END 
OF    EMBRYO 


WOLFFIAN 
DUCT 


PELVIS    OF 
URETER 


Fig.  28.— Reconstruction  of  caudal  end  of  human  embryo  of  11.5  mm.  (four  and  a  half 
weeks),  showing  pelvic  structures.     X  40.     (After  Keibel.) 


PLATE   XII. 


ALLANTOIC    DUCT. 
BLADDER 


GENITAL  TUBEROSITY- 


UROGENITAL   SINUS- 
URORECTAL   SEPTUM 


CAUDAL   END 
OF    EMBRYO 


END-GUT 
WOLFFIAN     DUCT 


.CHORDA    OORSALIS 


MEDULLARY    TUBE 


Fig.  29.— Reconstruction  of  caudal  end  of  human  embryo  of  14  mm.  (five  weeks).     X  20 
(After  Keibel.) 


GENITAL    FOLDS 


GENITO-URINARY    SINUS- 


GENITAL    RIDGES 


PROCTOD/CUM 


Fig.  30. — Human  female  foetus,  3.4  cm.  long,  vertex-coccygeal  measure. 
The  external  perineal  folds  separate  the  anal  invagination  from  the  urogenital 
opening.     (Kollmann.) 


UROGENITA 

SINUS 


INTERNAL 
PERINEAL 
FOLD 


PROCTO0>CUM 


Fig.  31.— Section  of  pelvis  of  human  foetus,  showing  atresia  recti.     (Esraarch.) 


PLATE    XIII. 


MEDULLARY   TUBE 


CHORDA    DORSALIS 


MESOTHELIUM 


ENTODERMAL   TUBE    OF 
ALIMENTARY    CANAL 


Fig.  32.— Schematic  diaKnuiis.   illustrating  the  vertebral  nuseutery.      A,  ear- 
lier;  B,  later  condition.     (Minot.) 


MIDDLE    LOBE  OF 

THYROID     GLAND 

LATERAL    LOBE    OF 

THYROID    GLAND 


TRACHEA 
LUNG 


RIGHT    LOBE 
OF   LIVER 


OMPHALO- 
MESENTERIC 
DUCT 


SALIVARY 
GLANDS 


PHARYNGEAL 

POUCHES 
THYMUS 
GLAND 


STOMACH 


PANCREAS 
LEFT  LOBE 
OF    LIVER 


SMALL 
INTESTINE 


LARGE 
INTESTINE 


Fig.  33. — Schema  of  alimentary  canal  and 
accessory  organs,  derived  from  same.  (After 
Bonnet.) 


YPOPHYSIS 


ALLANTOtS 


WOLFFIAN 
DUCT 


Fig.  34. — Eeconstruction  of  alimentary  canal 
of  human  embryo  of  4.2  mm.    X  24.     (After  His.) 


PLATE   XIV. 


CESOPHAGUS 
TRACHEA    AND    LUNG 


PANCREAS 


WOLFFIAN    DUCT 


PRIMITIVE    LARYNX 


PITUITARY    FOSSA 


HEPATIC    DUCT 


VITELLINE    DUCT 


ALLANTOIS 


END-GUT 


Fig.  35.— Reconstruction  of  alimentary  canal  of  human  embrvo  of  7  mm    ("twentv- 
eight  days).     X  12.     (After  His.)  •  v  J- 


CESOPHAGUS 
TRACHEA 


STOMACH 
PANCREAS- 


PITUITARY    FOSSA 
TONGUE 


HEPATIC    DUCT 


C>ECUM 

GENITAL    EMINENCE 

ANAL    INVAGINATION 
CAUDAL    END    OF 
EMBRYO 


five  £ys  (fc^  mm"''x  t"  (iS^'r  ""'  ''  '""'"  '""'"'"  "'  ""''^' 


PLATE   XV. 


SEROUS  NON-VASCU- 
LAR FOLD  BETWEEN 
ILEUM  AND  DIVER- 
TICULUM 


ROOT    OF    MECKEL'S 
DIVERTICULUM 


OMPHALO  -MESEN- 
TERIC ARTERY  EX- 
TENDING UPON 
DIVERTICULUM 


Fig.  37. — Human  adult  ileum  with  Meckel's  diverticulum.     Ileo-diverticnlar  serous  fold  and 
persistent  omphalo-mesenteric  artery.     (Columbia  University  Museum,  No.  1803.) 


Fig.  38. — Human  adult  ileum,  with  Meckel's  diverticulum. 
Museum,  No.  745.) 


(Columbia  University 


O  u  S  O 


> 

X 

w 

h 
Pu 


INTRODUCTION.  25 

This  is  the  permanent  condition  of  the  terminal  openings  of  the 
alimentary  and  genito-urinary  tracts  in  the  lower  vertebrates.  It 
is  found  in  certain  fishes,  in  all  amphibia,  reptiles  and  birds,  and 
occurs  also  in  one  order  of  mammals,  the  monotremes.  In  man 
and  mammals  generally  the  anal  orifice  is  separated  from  the 
genito-urinary  opening,  lying  dorsad  of  the  same  and  provided 
with  special  sphincters.  Only  in  the  monotremes  do  the  anus 
and  the  genito-urinary  tract  open  into  a  common  cloaca  sur- 
rounded by  a  sphincter  common  to  the  anal  and  genito-urinary 
openings  (sphincter  cloacae).  In  birds,  reptiles,  amphibia  and 
many  fishes  (especially  the  Plagiostomata)  this  cloacal  formation 
is  the  rule.  In  many  fishes,  especially  the  Teleosts,  the  anus  and 
the  genito-urinary  openings  are  separate,  as  in  mammals,  but  their 
position  is  reversed,  the  anus  being  ventral,  while  the  genito-uri- 
nary opening  is  placed  dorsally. 

Fig.  23  shows  the  cloaca  in  a  female  specimen  of  Iguana 
tuberculata.  The  ventral  wall  of  the  cloaca  has  been  divided  to 
the  left  of  the  median  line  and  turned  over  to  the  right,  carrying 
with  it  the  cloacal  opening  of  the  bladder.  The  termination  of 
the  alimentary  canal  opens  into  the  cloaca  from  above. 

A  transverse  fold  of  the  mucosa  separates  this  upper  compart- 
ment of  the  cloaca  (coprodasum)  from  a  lower  space  (urodseum) 
which  receives  in  its  dorsal  wall  the  openings  of  the  two  oviducts 
and  immediately  above  them — upon  two  papillae — the  openings  of 
the  ureters,  while  the  ventral  wall  contains  the  cloacal  opening 
of  the  bladder. 

The  right  ovary  has  been  removed — to  show  the  abdominal  open- 
ing of  the  right  oviduct — by  dividing  the  mesovarian  peritoneal 
fold. 

Fig.  24 — taken  from  a  preparation  of  the  hen — shows  the  typical 
arrangement  of  the  female  genito-urinary  tract  and  cloaca  in  the 
birds. 

The  terminal  portion  of  the  ahmentary  canal,  in  entering  the 
cloaca,  forms  an  expanded  upper  cloacal  compartment  for  the  ac- 
cumulation of  the  excreta,  called  the  coprodseum. 


26  ABDOMINAL  CAVITY  AND  PERITONEUM. 

It  is  separated  by  a  prominent  mucous  fold  from  the  central 
compartment,  or  urodxum  which  receives  the  terminations  of  the 
two  ureters  and  of  the  single  (left)  oviduct.  A  second  fold  forms 
the  distal  limit  of  the  urodseum  and  separates  it  from  the  lowest 
cloacal  compartment,  the  prododseum. 

Fig.  25  shows  the  male  genito-urinary  tract  and  the  cloaca  in 
the  monotreme,  Platypus  anatinus.  The  cloaca  is  a  spacious  sac 
formed  by  the  confluence  of  the  rectum  and  the  genito-urinary 
sinus. 

The  penis,  consisting  of  two  large  cavernous  bodies,  is  contained 
in  a  fibrous  sac  which  arises  from  the  junction  of  the  genito- 
urinary sinus  and  the  cloaca,  and  is  continued  into  the  ventral 
wall  of  the  cloaca  near  its  termination  by  an  opening  through 
which  the  penis  can  pass  into  the  cloaca  and  beyond  the  external 
cloacal  aperture. 

The  semen  enters  the  penis  at  its  root  through  a  narrow  opening 
situated  close  to  the  junction  of  genito-urinary  sinus  and  cloaca. 

For  a  short  period,  therefore,  the  human  embryo  and  the  em- 
bryos of  the  higher  mammalia  present  conditions  which  correspond 
to  the  permanent  structure  of  the  parts  in  these  lower  vertebrates. 
In  human  embryos  of  11.5  mm.  cervico-coccygeal  measure  (32- 
33  days)  (Fig.  28),  the  cloaca  appears  as  a  short  sac  continuous 
dorsad  with  the  intestine,  ventrad  with  the  rudiment  of  the 
urinary  bladder.  The  larger  portion  of  the  caudal  gut  (postanal 
gut)  has  disappeared,  having  been  reduced  to  a  thin  epithelial 
strand  which  gradually  becomes  entirely  absorbed.  Only  the 
proximal  portion  of  the  end-gut  is  used  for  the  development  of  the 
cloaca,  which,  however,  at  first  has  no  external  opening  (Fig.  28). 

The  tail  end  of  the  embryo  becomes  more  extended  and  between 
it  and  the  umbilical  cord  an  interval  appears  in  which  the  genital 
protuberance  develops.  Behind  this  point  the  ventral  cloacal 
wall  is  formed  by  the  cloacal  membrane. 

A  considerable  interval  also  develops  between  the  points  of  en- 
trance into  the  cloaca  of  the  intestine  proper  and  of  the  allantoic 
stalk  (urinary  bladder).     The  growth  of  the  mesoderm  pushes 


INTRODUCTION.  27 

the  intestine  against  the  sacral  vertebrae,  while  the  stalk  of  the 
allantois  with  the  rudimentary  urinary  bladder  is  forced  against 
the  ventral  abdominal  wall.  These  changes  prepare  the  way  for 
the  first  appearance  of  the  genito-urinary  sinus.  The  neck  of  the 
embryonic  bladder  elongates  and  receives  the  ducts  of  the  urinary 
and  genital  glands  (Fig.  29).  In  embryos  of  14  mm.  cervico- 
coccygeal  measure  (36-37  days)  (Figs.  29  and  30),  the  genito- 
urinary sinus  perforates  the  cloacal  membrane  on  the  ventral 
aspect  of  the  genital  protuberance,  forming  the  uro-genital  cleft. 
The  rectum  remains  closed  for  a  few  days  longer.  The  perfora- 
tion is  preceded  by  the  formation  of  a  transverse  ectodermal  redu- 
plication, producing  a  depression  called  the  transverse  anal  fissure. 
This  depression  increases  in  depth  until  a  distinct  anal  invagi- 
nation results,  known  as  the  proctodxum,  which  grows  as  a  funnel- 
shaped  fossa  toward  the  blind  termination  of  the  endgut.  In 
embryos  of  25  mm.  cervico-coccygeal  measure  (8i-9  weeks)  the 
intestine  still  ends  in  a  blind  pouch.  The  anus  is,  therefore, 
independent  of  the  end-gut  in  its  development.  It  is  derived 
from  the  ectoderm  and  its  production  is  analogous  to  the  forma- 
tion of  the  oral  cavity  by  means  of  the  ectodermal  invagination 
called  the  stomadxum. 

Finally  the  cloaca  is  converted  into  a  ventral  tube  from  which 
part  of  the  urinary  bladder,  the  urethra  and  genito-urinary  sinus 
develop,  and  a  dorsal  tube  from  which  the  rectum  is  derived. 
This  double  disposition  of  the  cloaca  is  accomplished  by  gradual 
changes  in  the  entoderm  and  mesoderm.  The  entoderm  prolifer- 
ates until  a  partition  is  formed  which  separates  the  two  divisions 
of  the  cloacal  tube  from  each  other,  and  the  mesoderm  likewise 
increases,  surrounding  the  newly  formed  entodermal  tubes  with 
tissue  from  which  the  muscles,  connective  tissue  and  blood  vessels 
of  the  parts  are  derived  (Figs.  28  and  29). 

This  partition,  the  septum  uro-rectale,  develops  symmetrically 
on  each  side,  appearing  first  as  paired  folds  on  the  right  and  left 
sides  called  the  internal  perineal  folds  (Figs.  28  and  29).  When 
these  folds  have  reached  the  cloacal  membrane  they  complete  the 


28  ABDOMINAL  CAVITY  AND  PERITONEUM. 

separation  of  the  cloaca  into  two  adjacent  canals.  Each  of  these 
canals  is  still  closed  caudad  by  its  respective  portion  of  the  cloacal 
membrane,  now  divided  into  an  anal  and  uro-genital  segment. 
These  two  portions  of  the  original  cloacal  membrane  become  per- 
forated separately,  the  uro-genital  before  the  anal.  Hence  the 
external  opening  of  the  uro-genital  sinus  is  the  first  to  appear,  to 
be  followed  by  the  anal  perforation.  The  internal  perineal  folds 
are  supplemented  by  the  formation  of  similar  external  folds,  ridges 
of  mesoderm  tissue  which  surround  the  anal  orifice  in  the  form  of 
a  low  wall  and  thus  deepen  the  anal  ectodermal  invagination  into 
the  fossa  of  the  proctodseum. 

These  developmental  stages  in  the  formation  of  the  end-gut  are 
of  importance  because  they  offer  the  explanation  of  the  patho- 
logical conditions  which  result  from  an  arrest  of  development  and 
from  the  failure  of  either  the  uro-genital  or  anal  opening  to  form 
in  the  usual  manner.  These  malformations  must  date  back  to  an 
early  stage,  and  probably  have  their  inception  in  disturbances 
occurring  in  the  normal  development  between  the  15th  and  23d 
day  (embryos  of  3-6  mm.).  Perhaps  in  some  cases  of  atresia  there 
may  be  a  secondary  obliteration  of  a  previously  formed  opening. 
In  Fig.  31  the  proctodaeum  persists  but  the  perforation  of  the 
anal  membrane  into  the  end-gut  has  not  occurred.  The  ectoderm 
of  the  anal  fossa  and  the  intestinal  entoderm  remain  separated  by 
a  transverse  mesodermal  partition.  Different  degrees  of  this  mal- 
formation are  observed.  The  layer  separating  the  skin  from  the 
blind  end  of  the  rectum  may  be  so  thin  that  the  meconium  con- 
tained in  the  latter  can  be  felt  through  it.  On  the  other  hand 
the  rectum  may  terminate  high  up  in  a  blind  pouch,  which  is 
separated  from  the  skin  by  a  distance  of  several  centimeters. 

We  may  now  briefly  consider  the  genetic,  histological  and  me- 
chanical conditions  which  the  above-outlined  course  of  develop- 
ment imposes  on  the  alimentary  tract. 

The  ectoderm  forms  the  superficial  covering  of  the  embryo  and 
in  the  dorsal  axial  line  develops  the  medullary  groove  which 
subsequently  becomes  converted  into  the  cerebro-spinal  axis  by 


INTRODUCTION.  29 

closure  of  the  medullary  plates  and  inclusion  of  the  neural  tul)e 
within  the  surrounding  mesoblast  (Fig.  18).  The  entoderm 
forms  the  epithelial  lining  of  the  interior  of  the  alimentary  canal 
and  its  appendages  and  derivatives  (Fig.  19).  The  mesoderm 
furnishes  the  skeletal,  muscular  and  vascular  systems.  At  first 
single,  Uke  the  two  remaining  layers  of  the  blastoderm,  the  meso- 
derm splits  early  on  each  side  of  the  chorda  dorsalis  into  two 
layers,  including  between  them  spaces  which  after  coalescence 
form  the  'primitive  'pleuro-j)erit(me(il  or  body-cavity  (Fig.  20).  One 
of  these  mesodermal  layers  bounding  this  space  becomes  closely 
connected  with  the  ectoderm,  forming  the  somatopleure  or  body 
wall,  while  the  other  joins  the  entoderm  to  complete  the  wall  of 
the  alimentary  canal,  forming  the  sfplanchruypleure.  In  the  course 
of  further  development  the  edges  of  these  two  layers  approach 
each  other  ventrally  in  the  median  line  and  finally  fuse. 

The  products  of  this  fusion  are  two  epithelial  tubes,  one  included 
within  the  other,  with  walls  reinforced  by  tissue  derived  from  the 
two  layers  of  the  mesoderm.  The  internal  or  entodermal  tube  is 
of  much  smaller  diameter  than  the  outer  or  ectodermal  tube,  but 
much  longer.  The  walls  of  the  two  tubes  are  placed  in  contact 
with  each  other  by  their  mesodermal  elements  dorsally  in  the 
axial  line,  but  elsewhere  are  separated  from  each  other  by 
the  body-caWty  (except  in  the  region  of  the  ventral  mesogaa- 
trium). 

The  splanchnopleure  is  not  so  wide  as  the  somatopleure.  As  it 
closes  in  the  ventral  median  line  it  includes  the  deepest  or  ento- 
dermal layer.  It  now  forms  a  tube  whose  walls  are  composed 
superficially  of  mesoderm  (splanchnopleure)  while  the  lumen  is 
lined  by  epitheUnm  derived  from  the  entoderm.  This  tube  is  the 
primitive  enteric  or  alimentary  canal.  The  somatopleuric  layers 
bounding  the  body  cavity  take  a  wider  sweep  and  after  they  have 
united  ventrally  in  the  median  line  they  embrace  a  much  more 
extensive  space,  the  primitive  body  cavity  or  ccslom.  The  walls  of 
this  space  are  largely  made  up  of  the  skeletal  and  muscular  ele- 
ments developed  firom  the  mesoderm  of  the  somatopleure,  cov- 


30     .  ABDOMINAL  CAVITY  AND  PERITONEUM, 

ered  superficially  by  the  common  ectodermal  investment  of  the 
body.  It  will  be  seen  that  the  enteric  tube  thus  becomes  in- 
cluded within  the  wider  and  more  capacious  coelom  cavity. 

Both  the  somatic  and  the  splanchnic  leaf  of  the  mesoderm 
consist  at  first  solely  of  a  layer  of  flattened  epithelial  cells,  the 
mesothelium.  But  very  early  this  tissue  is  increased  to  form  a 
massive  layer  by  direct  development  from  the  mesothelium.  The 
new  mesodermal  cells  thus  produced  constitute  the  mesenchyma, 
which  includes  the  whole  of  the  mesoderm  of  the  embryo  except 
the  mesothelial  Kning  of  the  coelom.  The  cells  of  the  mesen- 
chyma, connected  wath  each  other  and  with  the  mesothelial  cells 
by  protoplasmic  processes,  are  not  as  close  together  as  in  an  epi- 
thelium and  do  not  form  a  continuous  membrane.  By  migration 
and  multiplication  a  large  mass  of  mesodermal  tissue  is  produced 
which  fills  the  entire  space  between  the  mesothelium  and  the 
primary  germ  layers.  The  mesenchymal  tissue  between  the  meso- 
thelium and  the  ectoderm  forms  the  mass  of  the  skeletal,  muscu- 
lar and  vascular  systems.  The  mesenchymal  tissue  between  the 
mesothelium  and  the  entoderm  forms  an  important  constituent 
of  the  alimentary  canal  and  of  its  appendages.  The  entoderm 
furnishes  the  internal  epithelial  lining  of  the  tube  upon  which 
the  performance  of  the  specific  physiological  function  of  the  en- 
tire apparatus  depends.  This  epithelial  tube  is  covered  from 
without  by  the  splanchnic  mesoderm.  The  mesodermal  elements 
thus  added  to  the  enteric  entodermal  tube  consist  of  connective 
tissue  and  muscular  fibers.  The  latter,  arranged  in  the  form  of 
circular  and  longitudinal  layers,  control  the  contractility  of  the 
tube  and  regulate  the  propulsion  of  the  contents.  The  connec- 
tive tissue  of  the  splanchnic  mesoderm  appears  as  an  intermediate 
layer  uniting  the  epithelial  lining  and  the  muscular  walls.  Situ- 
ated thus  between  the  mucous  and  muscular  coats  of  the  intes- 
tine this  layer  is  known  as  the  submucosa.  It  contains,  imbedded 
in  its  tissue,  the  glandular  elements  of  the  intestine  derived  from 
the  entodermal  epithelium,  and  the  blood  vessels,  lymphatics  and 
nerves.    The  second  chief  function  of  the  splanchnic  and  somatic 


INTRODUCTION.  31 

mesoderm  is  the  production  of  the  serous  membrane  investing  the 
body  cavity  and  its  contents  from  the  mesotheUum  Uning  the 
primitive  coelom.  This  mesotheUal  tissue,  differentiated  as  a 
layer  of  flattened  cells,  lines  the  interior  of  the  body  cavity  and 
covers  the  superficial  aspect  of  the  enteric  tube.  By  i^ubsequent 
partition  of  the  common  coelom  the  great  serous  membranes  of 
the  adult,  the  pleurae,  pericardium  and  peritoneum,  are  developed 
from  it. 

The  entodermal  enteric  tube  is,  as  already  stated,  closely  attached 
at  an  early  period  along  its  dorsal  surface  to  the  axial  rod  of 
mesoderm  containing  the  chorda  dorsalis  immediately  ventrad  of 
the  neural  canal.  In  the  earliest  stages,  just  after  the  splanchno- 
pleure  and  somatopleure  have  closed  to  complete  the  alimentary 
tube  and  body  cavity,  the  remnant  of  these  layers  extends  between 
the  ventral  abdominal  wall  and  the  ventral  surface  of  the  intestine 
forming  a  partition  which  divides  the  body  into  a  right  and  left 
half  (Fig.  32,  A.)  For  the  most  part  this  primitive  connection 
between  the  ventral  abdominal  wall  and  the  intestinal  tube  is  lost 
very  early.  The  stomach,  however,  is  always  connected  by  a 
ventral  mesogastrium,  from  which  the  lesser  omentum  is  derived, 
to  the  ventral  body  wall.  The  disappearance  of  the  ventral  me- 
sentery caudad  of  this  point  establishes  the  condition  indicated 
in  Fig.  32,  B.  The  entodermal  tube  and  the  surrounding  splanch- 
nic mesoderm  forming  the  intestinal  canal  is  attached  along  its 
dorsal  surface  to  the  axial  mesoderm  of  the  dorsal  mid-line.  The 
primitive  mesothelial  peritoneum  is  reflected  along  this  line  from 
the  internal  surface  of  the  body  wall  upon  the  ventral  and  lateral 
surfaces  of  the  intestine.  The  coelom  of  one  side  communicates 
ventrad  of  the  intestine  with  the  coelom  of  the  opposite  side. 
Hence  by  the  disappearance  of  the  ventral  mesentery  caudad  of 
the  stomach  the  paired  body-cavities  have  become  fused  into  a 
single  abdominal  cavity — while  cephalad  the  original  division  into 
right  and  left  halves  is  maintained  by  the  portion  of  the  ventral 
mesentery  which  attaches  the  stomach  to  the  ventral  abdominal 
wall.     The  mesodermal  tissue  which  at  this  time  attaches  the 


32  ABDOMINAL   CAVITY  AND  PERITONEUM. 

alimentary  tube  along  its  entire  extent  to  the  dorsal  wall  of  the 
coelom  carries  the  primitive  embryonic  arterial  vessel,  the  aorta. 
This  vessel  supplies  a  series  of  small  branches  to  the  intestine, 
which  reach  the  same  by  passing  ventrad  imbedded  in  the  meso- 
derm connecting  the  tube  to  the  dorsal  body  wall. 

With  the  further  development  of  the  alimentary  canal  a  gradual 
elongation  of  this  connecting  band  of  mesoderm  and  of  the  con- 
tained vessels  is  observed,  the  tube  itself  gradually  receding  from 
the  vertebral  axis.  The  early  broad  attachment  is  replaced  by  a 
narrower  stalk  into  which  the  mesoderm  is  drawn  out.  With 
this  narrowing  in  the  transverse  and  elongation  in  the  sagittal 
direction  the  connecting  tissue  assumes  the  character  of  a  thin 
membrane  with  two  free  serous  surfaces,  including  the  intestinal 
vessels  imbedded  between  them.  Coincident  with  this  elongation 
of  the  enteric  attachment  and  its  narrowing  in  the  transverse  di- 
rection the  primitive  intestine  becomes  more  completely  invested 
by  the  serous  lining  membrane  of  the  coelom  cavity.  In  this 
stage  we  can  speak  of  the  double-layered  membrane  attaching 
the  tube  to  the  dorsal  body  wall  and  carrying  the  intestinal  blood- 
vessels as  the  primitive  dorsal  mesentery.  The  intestinal  canal 
itself  is  invested  by  serous  membrane  except  along  a  narrow  strip 
of  its  dorsal  border  where  the  mesentery  is  attached  and  where 
the  vessels  reach  the  intestine.  We  can  now  distinguish  the 
serous  lining  membrane  of  the  abdominal  cavity,  derived  from 
the  mesothelium  of  the  splanchnic  and  somatic  mesoderm  as  the 
peritoneum.  The  membrane  presents  the  following  topographical 
subdivisions : 

1.  Parietal  Peritoneum,  lining  the  inner  surface  of  the  abdom- 
inal walls. 

2.  Visceral  Peritoneum,  investing  the  external  surface  of  the 
intestine  and  its  derivatives. 

3.  Mesenteric  Peritoneum,  connecting  these  two,  carrying  the 
intestinal  blood  vessels  and  lymphatics  and  acting  as  a  suspensory 
support  to  the  alimentary  canal. 

The  dorsal  mesentery  in  fishes,  amphibia  and  reptiles  contains 


INTRODUCTION.  33 

smooth  muscular  fibers  derived  from  the  mesoderm.  These  bands 
of  smooth  muscle  fibers  are  also  encountered,  though  less  well  de- 
veloped, in  the  mesentery  of  birds  and  mammals.  The  so-called 
"  suspensory  muscle  of  the  duodenum  "  belongs  to  this  category. 
It  consists  of  a  few  strands  of  unstriped  muscular  and  fibrous 
tissue  which  passes  from  the  prseaortal  tissue  around  the  origin  of 
the  superior  mesenteric  artery  and  coeliac  axis  to  the  duodeno- 
jejunal angle.  Fasciculi  from  this  band  may  penetrate  into  the 
root  of  the  mesentery  (Gegenbaur). 

Similar  muscular  fasciculi  have  been  observed  in  the  peritoneal 
folds  of  the  ileo-csecal  junction  (Luschka)  and  in  the  mesorectum 
— forrding  in  the  latter  situation  the  recto-coccygeal  muscles  of 
Treitz,  and  in  the  female  the  recto-uterine  muscles. 

In  its  earlier  stages  the  primitive  common  mesentery  forms  a 
membrane  which  carries  the  intestinal  blood  vessels  between  its  two 
layers,  surrounds  the  embryonic  alimentary  canal  and  attaches 
the  same  to  the  ventral  aspect  of  the  chorda  dorsalis  and  aorta. 
This  is  the  permanent  condition  in  many  of  the  lower  vertebrates 
in  which  the  intestinal  tube  is  suspended  by  a  simple  dorsal 
mesentery,  a  condition  which  is  repeated  by  the  embryos  of  man 
and  the  higher  vertebrates.  From  this  primitive  common  mesen- 
tery are  derived,  by  further  development,  displacement  and  adhe- 
sion, all  the  other  mesenteries,  omenta  and  peritoneal  folds  of  the 
adult.  The  character  and  degree  of  these  subsequent  changes  is 
determined  by  the  increase  in  length  and  change  in  position  of 
the  intestine  and  the  growth  of  large  organs,  like  liver,  spleen 
and  pancreas.  Many  portions  of  the  intestinal  canal,  at  first  sus- 
pended by  the  mesentery  and  freely  movable  within  the  ab- 
dominal cavity,  become  later,  by  secondary  adhesion,  firmly  con- 
nected with  adjacent  portions  of  the  tube  or  with  the  abdominal 
parietes. 

In  certain  of  the  lower  vertebrates  (fishes)  large  sections  of  the 
intestine  lie  entirely  free  within  the  abdomen,  their  only  con- 
nection with  the  parietes  being  afforded  by  the  blood  vessels. 
This  condition  depends  upon  absorption  of  the  original  mesentery. 

8 


34  ABDOMINAL  CA  VITT  AND  PERITONEUM. 

A  similar  process,  though  much  more  circumscribed,  is  observed 
in  the  omenta  of  many  mammals,  which  appear  perforated  at  sev- 
eral points. 

Derivatives  of  the  Entodennal  Intestinal  Tube. — The  entodermal 
epithelium  is  physiologically  the  characteristic  element  of  the 
alimentary  canal.     Besides  lining  the  entire  internal  surface  of 
the  tube  it  gives  rise  by  budding  and  protrusion  from  the  intes- 
tinal canal  to  a  series  of  organs  which  from  the  mode  of  their 
development  must  be  regarded  as  diverticular  or  derivatives  of  the 
alimentary   canal   (Figs.    33,  34,  and  35).     These   organs,  pro- 
ceeding in  order  cephalo-caudad,  are  the  following  : 
The  salivary  glands. 
Thymus  and  thyroid. 
The  lungs. 
Pancreas. 
Liver. 

The  epithelium  of  all  these  structures  is  derived  from  the  prim- 
itive entoderm  of  the  intestinal  tube,  except  the  epithelium  of  the 
salivary  glands,  which,  being  derived  from  the  stomadseal  invagi- 
nation, is  ectodermal  in  character.  We  have  previously  noted  the 
general  history  and  appearance  of  the  yolk-sac  and  its  connection 
by  means  of  the  vitello-intestinal  duct  with  the  intestine.  In 
contradistinction  to  the  adult  organs  just  noted  the  yolk-sac  or 
umbilical  vesicle  is  merely  a  temporary  embryonal  appendage  to 
the  alimentary  canal.  It  also  differs  from  them  in  the  fact  that 
it  is  not  an  extension  or  budding  from  the  completed  intestinal 
tube,  like  the  liver  and  pancreas,  but  indicates,  by  the  implanta- 
tion of  the  duct  (Fig.  21),  the  last  point  at  which  closure  of  the 
intestinal  canal  takes  place,  when  after  obliteration  of  the  duct 
the  separation  of  the  intestine  from  the  yolk-sac  is  completed. 

The  segment  of  the  primitive  alimentary  canal  cephalad  of  the 
attachment  of  the  vitello-intestinal  duct  gives  rise  to  the  pharynx, 
oesophagus,  stomach,  proximal  portion  of  small  intestine  proper 
and  its  derivatives,  the  liver  and  pancreas. 

The  portion  situated  caudad  of  the  duct  produces  the  rest  of  the 


INTRODUGTJON.  35 

small  and  all  of  the  large  intestine  (Figs,  33  and  35).  At 
times  in  man  and  other  mammals  (cat)  the  vitello-intestinal  duct 
does  not  become  absorbed,  but  persists  and  continues  to  develop 
as  a  part  of  the  small  intestine,  forming  the  blind  pouch  or 
appendage  known  as  MeckeVs  diverticulum  (Figs.  37  and  38). 
This  diverticulum  may  vary  in  length  from  1.5  to  15  cm.  It 
either  projects  freely  into  the  abdominal  cavity  as  a  pouch  arising 
from  the  convex  border  of  the  small  intestine  opposite  to  the 
mesenteric  attachment,  or  else  it  reaches  the  abdominal  wall  at 
the  umbilicus  and  is  attached  to  the  same.  In  a  few  instances  it 
has  not  terminated  in  a  blind  pouch,  but  has  remained  open  at 
the  umbilicus,  in  which  case  the  aperture  discharges  intestinal 
contents.  Sometimes  the  process  of  obliteration  which  normally 
leads  to  the  absorption  of  the  vitello-intestinal  duct  extends  to 
the  adjoining  segment  of  the  small  intestine,  resulting  in  oblit- 
eration of  the  intestinal  lumen  and  consequent  obstruction  at 
this  point. 

The  intestinal  opening  of  the  diverticulum  is  situated  at  a  vary- 
ing distance  above  the  ileo-colic  junction,  ranging  from  27.5  cm. 
to  290  cm.,  with  an  average  of  107  cm. 

While  the  obliteration  and  complete  absorption  of  the  duct  is 
normal  in  nearly  all  vertebrates,  a  remnant  persists  in  some 
birds,  in  which  a  short  csecal  pouch  {diverticulum  caecum  vitelli)  is 
found  at  about  the  middle  of  the  small  intestine.  A  portion  of 
the  vitello-intestinal  duct  thus  persists  throughout  life  in  some 
wading  and  swimming  birds.  Figs.  39  and  40  show  this  condition 
in  the  small  intestine  of  Urinator  lumme  and  imber,  the  red- throated 
loon  and  the  great  northern  diver.  In  other  birds,  however, 
such  as  birds  of  prey,  song  birds,  etc.,  the  duct  is  absorbed  and 
disappears  completely. 

In  order  to  complete  the  embryological  history  of  the  alimen- 
tary canal  it  is  necessary  to  take  brief  account  of  another  struc- 
ture derived  from  it,  namely  the  allantois.  Its  significance  to 
the  adult  organism  is  seen  in  connection  with  the  genito-urinary 
tract,  the  urinary  bladder  being  formed  by  its  persistent  portion. 


36  ABDOMINAL  CAVITY  AND  PERITONEUM. 

In  the  embryo,  however,  it  has  important  nutritive  and  respira- 
tory functions.  In  the  embryos  of  the  higher  vertebrates  nutri- 
tion depends  only  in  the  earhest  stages  upon  the  yolk-sac  of  the 
ovum,  over  which  a  vascular  network  extends. 

Very  soon  the  caudal  portion  of  the  primitive  intestine  devel- 
ops a  vascular  sac-like  outgrowth  (Figs.  21  and  41).  This  pouch 
forms  the  allantois.  It  is  intimately  connected  with  embryonal 
respiration,  and  probably  also  forms  a  reservoir  which  receives 
the  secretion  of  the  primitive  kidney.  This  foreshadows  the 
final  destiny  of  the  proximal  intra-abdominal  portion  of  the 
allantoic  sac  which  persists  and  is  converted  into  the  urinary 
bladder  of  the  adult. 

The  allantois  is  present  in  Amphibia  but  is  very  small.  In 
Amniota  ^  it  is  large  and  grows  around  the  embryo.  In  those  of 
the  higher  vertebrates  which  are  developed  within  an  egg  (rep- 
tiles, birds  and  monotremes)  the  sac  of  the  allantois  comes  to  lie 
beneath  the  egg-shell  and  acts  as  a  respiratory  organ.  In  the 
higher  mammalia,  developed  within  the  uterus,  the  allantois  be- 
comes attached  by  vascular  villi  to  the  uterine  wall  and  estab- 
Hshes  a  vascular  connection  between  the  foetal  and  maternal 
blood  vessels.  In  this  way  the  allantoic  placenta  is  formed  (Fig. 
41).  The  placenta,  as  just  stated,  is  absent  in  the  monotremes 
and  is  only  slightly  developed  in  marsupials,  in  which  animals 
the  foetus  develops  to  maturity  in  the  marsupial  pouch  after 
leaving  the  uterus.  These  animals  are  therefore  distinguished 
as  Aplacenialia  from  the  remaining  higher  mammals  in  which 
the  allantoic  placenta  develops  and  which  are  hence  called  the 
Placentalia. 

Summary. — To  recapitulate,  therefore,  the  intestinal  tube  gives 
origin  to  two  kinds  of  appendages  or  derivatives  : 

'  In  the  embryos  of  reptiles,  birds  and  mammals  folds  of  the  somatoplenre  arise  exter- 
nally to  the  constricting  furrows  by  means  of  which  the  embryo  is  gradually  separated  from 
the  yolk-sac,  with  the  resulting  formation  of  the  intestinal  and  abdominal  walls.  These 
folds,  situated  at  the  head,  tail  and  on  the  sides,  grow  upwards  and  finally  meet  and  unite 
to  form  a  membranous  sac  called  the  amnion.  Hence  these  higher  vertebrates  (reptiles, 
birds  and  mammals)  are  called  Amniota,  in  contradistinction  to  fishes  and  amphibia  who 
have  no  amnion  and  are  hence  known  as  Anamnia. 


INTRODUCTION.  37 

1.  Organs  of  the  adult  body,  derived  by  budding  from  the  ah- 
mentary  entodermal  epithelium,  in  the  form  of  pouch-like  diver- 
ticula which  follow  the  glandular  type  of  development  and  be- 
come secondarily  associated  with  mesodermal  elements.  These 
organs  are  again  of  two  kinds  : 

(a)   Organs  which  retain  their  original  connection  with  the  lumen 
of  the  digestive  canal : 
The  salivary  glands," 

The  liver,  I     Connected  by  their  ducts  with  the  diges- 

The  pancreas,  tive  canal. 

The  lungs, 

which  open  by  means  of  the  trachea  and  the  laryngeal  aper- 
ture into  the  pharyngeal  cavum. 

(6)  Organs  which  lose  their  ^primitive  connection  with  the  alimentary 
canal. 

Thymus  and  Thyroid  Gland. 

2.  Embryonic  appendages  of  the  alimentary  tract. 

(a)  The  vitello-intestinal  or  omphalo-mesenteric  duct  and  the 
yolk-sac  or  umbilical  vesicle.  This  structure  does  not  form  as  an 
extension  from  the  intestinal  tube  after  the  same  has  been  closed 
by  coalescence  of  the  splanchnopleure  in  the  ventral  mid-line, 
but  is  the  result  of  the  folding  in  of  the  layers  of  the  embryonic 
germinal  area,  by  means  of  which  the  body-rudiment  is  con- 
stricted off  from  the  yolk-sac.  The  reduced  channel  of  communi- 
cation forms  the  vitello-intestinal  duct.  In  the  vast  majority  of 
vertebrates  this  disappears  completely  by  absorption  in  the  course 
of  further  development.  It  may  persist  in  part  abnormally  as 
Meckel's  diverticulum.  In  a  few  birds  its  proximal  portion  re- 
mains normally  as  a  small  blind  pouch  attached  to  the  free 
border  of  the  small  intestine. 

[b)  The  allantois.  This  is  a  hollow  outgrowth  from  the  em- 
bryonic intestinal  canal  of  the  higher  vertebrates,  performing  im- 
portant functions  in  connection  with  the  early  nutrition  of  the 
embryo.  In  the  course  of  subsequent  development  its  proximal 
portion,  situated  within  the  abdominal  cavity,  becomes  converted 


38  ABDOMINAL   CAVITY  AND  PERITONEUM. 

into  the  urinary  bladder.  In  mammals  it  loses  its  original  con- 
nection with  the  intestinal  canal  and  is  assigned  entirely  to  the 
genito-urinary  tract.  In  some  of  the  lower  vertebrates,  amphibia 
and  reptiles  it  retains  its  connection  with  the  ventral  wall  of  the 
cloaca  throughout  life.  (See  Fig.  42,  genito-urinary  tract  of 
Iguana  tuberculata.) 

After  the  intestinal  canal  has  become  separated  from  the  yolk- 
sac  it  forms  at  first  a  straight  tube,  running  cephalo-caudad  beneath 
the  chorda  dorsalis.  In  most  forms,  however,  the  intestine  grows 
much  more  rapidly  in  length  than  the  body-cavity  of  the  embryo 
in  which  it  is  contained.  Hence  the  intestine  is  forced  to  form 
coils  or  convolutions. 

The  entire  alimentary  canal,  from  the  mouth  to  the  anus,  can 
be  separated  into  the  following  divisions  and  subdivisions : 

I.  Foregut,  including 

1.  The  oral  cavity. 

2.  The  pharynx. 

3.  The  oesophagus. 

4.  The  stomach. 

II.  Midgut,  closely  associated  at  its  beginning  with  the  liver 
and  pancreas. 

It  extends  between  the  pyloric  extremity  of  the  stomach  and 
the  beginning  of  the  last  segment,  the  endgut,  frequently  sepa- 
rated from  both  by  ring-like  aggregations  of  the  circular  muscu- 
lar fibers  and  corresponding  projections  of  the  mucous  membrane 
(pyloric  and  ileo-colic  valves). 

The  midgut  is  usually  the  longest  portion  of  the  intestinal  tube. 

III.  Endgut,  the  last  segment  of  the  intestinal  canal,  courses 
through  the  pelvic  portion  of  the  body  cavity.  From  this  short 
end-piece  are  developed:  (1)  The  colon,  sigmoid  flexure  and 
rectum ;  (2)  the  cloaca  with  the  uro-genital  sinus  and  the  duct  of 
the  allantois. 


PART  I. 

ANATOMY  OF  THE  PERITONEUM  AND 
ABDOMINAL  CAVITY. 

For  the  purpose  of  studying  the  adult  human  peritoneum  it  is 
in  the  first  place  absolutely  necessary  to  obtain  a  correct  appre- 
ciation of  the  disposition  of  the  chief  viscera  within  the  abdomi- 
inal  cavity  and  of  their  mutual  relations.  In  the  second  place  the 
visceral  vascular  supply  of  the  abdomen  must  be  carefully  con- 
sidered in  order  to  correctly  appreciate  certain  important  relations 
of  the  peritoneal  membrane. 

A  review  of  the  visceral  contents  of  the  abdomen  shows  that 
we  have  to  deal  chiefly  with  the  divisions  of  the  alimentary  tract 
below  the  oesophagus  and  the  structures  directly  derived  from  the 
same,  as  liver  and  pancreas,  or  associated  topographically  with  the 
alimentary  canal,  as  the  spleen.  Portions  of  the  urinary  and  re- 
productive systems  situated  within  the  abdominal  and  pelvic 
cavities  will  also  require  consideration. 

The  digestive  apparatus  as  a  whole  presents,  in  the  first  place, 
a  segment  designed  to  convey  the  food  to  the  stomach,  the  oesoph- 
agus— supplemented  in  mammalia  by  the  special  apparatus  of  the 
mouth  and  pharynx,  in  which  the  food  is  mechanically  prepared 
for  digestion  by  chewing  and  mixed  with  the  secretion  of  the 
salivary  glands. 

The  digestive  apparatuis  proper,  succeeding  to  the  oesophagus,  is 
usually  divisible  into  two  sections  differing  in  function  and  struc- 
ture. 

1.  The  STOMACH,  a  short  sac-like  dilatation,  in  which  chiefly 
nitrogenous  material  is  digested. 

2.  The  SMALL  INTESTINE,  a  long  and  usually  much  convoluted 
narrow  tube,  chiefly  devoted  to  the  digestion  of  starches,  fats  and 
sugars,  and  to  the  absorption  of  the  digested  matters. 

39 


40  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

In  some  of  the  lower  vertebrates,  as  the  Cyclostomata  (Fig.  43), 
Esox,  Belone,  etc.,  among  fishes  (Fig.  48),  Necturus  and  Proteus 
among  amphibians  (Figs.  50  and  51),  the  separation  of  the  digestive 
portion  of  the  alimentary  tract  into  stomach  and  small  intestine 
is  not  clearly  defined  (vide  infra,  p.  43). 

A  distinct  digestive  segment  may  even  be  entirely  wanting, 
owing  to  its  failure  to  differentiate  from  the  oesophagus  on  the 
one  hand  and  from  the  endgut  on  the  other.  In  such  forms  the 
entire  digestive  canal  appears  as  a  tube  of  uniform  caliber  extend- 
ing from  mouth  to  anus.  It  is  necessary  to  begin  with  these 
simple  structural  conditions  in  order  to  obtain  a  clear  conception 
of  the  disposition  of  the  viscera  in  the  adult  human  abdomen. 
Such  simple  arrangement  of  the  alimentary  tract  is  found  in  the 
embryo  of  man  and  of  the  higher  vertebrates,  and  similar  rudi- 
mentary types  are  encountered,  as  the  permanent  condition,  in 
some  of  the  lower  forms.  These  latter  are  especially  valuable  for 
purposes  of  study,  because  they  afford  an  opportunity  of  examin- 
ing directly,  as  macroscopic  objects,  structural  conditions  which 
are  found  only  as  temporary  embryonal  stages  during  the  develop- 
ment of  the  higher  mammalia  (Fig.  43). 

In  the  early  stages  the  alimentary  tract  of  the  mammalian  em- 
bryo consists  of  a  straight  tube  of  nearly  uniform  caliber  (Fig. 
44,  A),  extending  from  the  pharynx  to  the  cloaca,  along  the 
median  line  in  the  dorsal  region  of  the  body  cavity,  connected 
with  the  ventral  aspect  of  the  axial  mesoderm  by  a  membranous 
fold  forming  the  primitive  common  dorsal  mesentery.  Subse- 
quently differentiation  of  this  simple  tube  into  successive  segments 
takes  place,  marked  by  differences  in  shape  and  caliber  and  in 
histological  structure. 

The  first  indication  of  the  future  stomach  appears  early,  in 
human  embryos  of  from  5-6  days  (Figs.  44,  By  and  45 ;  for  later 
embryonal  stomach  forms  compare  also  Figs.  33,  35  and  36),  as  a 
small  spindle-shaped  dilatation  of  a  portion  of  the  primitive  en- 
todermal  tube,  placed  in  the  median  plane,  dorsad  of  the  embry- 
onic outgrowth  of  the   liver,  between  it   and   the   oesophagus. 


PLATE    XVIIT 


PERICARDIUM 


GASTRIC 
DILATATION 


INTESTINAL 
CANAL  WITH 
SPIRAL  FOLD 
OF    MUCOSA 


Fig.  44. — Schematic  diagram  representing 
tliree  stages  in  the  differentiation  of  the  mam- 
malian digestive  tract:  A.  Early  undiiieren- 
tiated  stage,  in  which  the  entire  canal  ai)]>ears 
as  a  tube  of  uniform  calibre.  15.  Spindle- 
shaped  gastric  dilatation.  C.  Typical  mam- 
malian gastric  dilatation. 


Fig.  43. — Entire  alimentary  canal  of 
the  lamjircy.  Petromyzoii  marinus,  below 
the  pericardium.  (Columbia  University 
Museum,  No.  1575.) 


PLATE    XIX. 


BILIARY    DUCT. 


WOLFFIAN    DUCT 


CESOPHAGUS 
LUNG 


STOMACH 


PANCREAS 
VITELLINE    DUCT 


ALLANTOIS 


WOLFFIAN    BODY 


Fig.  45. — Eecoustruction  of  human  embryo.     1,  2,  3,  4,  Gill-pouches.     (After  Fol.) 


PRIMORDIAL 
CRANIUM 


YOLK-SAC 


UMBILICAL 
CORD 
CAUDAL    GUT 
RENAL    BUD 


FORE-GUT 


BRANCHIAL   CLEFTS 


LUNG    BUD 


COMMON    DORSAL 
MESENTERY 

WOLFFIAN    BODY 


Fig.  46. — Alimentary  canal  of  human  embryo  of  5  mm.     X  15.     (Eecoustruction  after  His.) 


PLATE   XX. 


RECTAL  GLAND 


BENT  PROBE 
PASSED  INTO 
I  NTE  ST  INAL 
OPENING  OF 
RECTAL  GLAND 


FORE-GUT    DIVIDED 


VAS    DEFERENS 


END-GUT   WITH    SPIRAL 
MUCOUS    FOLD 


ROD  PASSED  INTO 

CLOACAL  OPENING  OF 
ALIMENTARY    CANAL 

PROBE  PASSED  INTO 
OPENING  OF  GENITO- 
URINARY     PAPILLA 

PROBE    IN    ABDOM- 
INAL   PORE 


Fig.  47. — Gallns  cnnin,  dog-shark,  ^.  Genitourinary  tract  and  cloaca  hi  situ. 
The  fore-gut  has  been  divided  just  caudad  of  the  communication  with  the  oral  cavity. 
(Columbia  University  Museum,  No.  1694.) 


PLATE    XXI. 


■XSOPHAGUS 


-OESOPHAGUS 


SLIGHT   GASTRIC 
DILATATION 


-MID-GUT 


U 


Fig.  48. — Alimentary  caual 
of  Belone,  pickerel.     (Nuhn.) 


Fig.  51. — Alimentary 
canal  of  Proteus  an- 
guineus.     (Nuhn.) 


ENTRANCE    TO     MOUTH 
WITH  OVERLYING 

BUCCAL    CIRRI 


ENDOSTYLE 


HEPATIC    CiECUM 


GONADIC    POUCHES 


STOMACH 


-STOMACH 


-INTESTINE 


Fig.  52. — Alimentary 
canal  of  Coluber  natrix. 
(Nuhn.) 


, SPLEEN 


NTESTINE 


PYLORODUODENAL 
JUNCTION 


»^      — ANUS 


Fig.  49. — Amphioxnti,  dissected  from 
the  ventral  side.  The  relatively  enor- 
mous pharvnx  occupies  more  than 
half  the  length  ol'  the  body.  The 
walls  are  seiiarali'd  by  the  gill-clefts, 
and  the  parallel  gill-bars  abut  at  the 
midveutral  line  on  the  endosli/le. 
(Willey,  after  Rathke.) 


PANCREAS 


—  MID-GUT 


END-GUT 


Fig.  50. — Kecturus  rnacnlatus,  mud-puppy.  Ali- 
mentary canal  and  appendages.  (Columbia  Uuiversity 
Museum,  No.  1454.) 


PLATE    XXII. 


• (ESOPHAGUS 


OeSO PHAGE O- GAS- 
TRIC   JUNCTION 


GASTRIC    MUCOUS 
MEMBRANE 


Fig.  53. — Human  adult.    Mucous  surface  of  cesophageo-j 
trie  junction.     (Columbia  University  Museum,  No.  1842.) 


GASTRIC    MUCOUb 
MEMBRANE 


THICKENED     CIRCULAR 
MUSCULAR  FIBRES 

OF    PYLORIC    VALVE 


DUODENUM 


Fig.  54. — Human  adult.      Pyloro-duodenal  junction  and 
jiyloric  valve  in  section.     (Columbia  University  Museum,  No. 

1842.) 


PLATE    XXIII. 


-ZSOPHAGUS 


INTESTINE 


Fig.  56. — Alimentary  canal  of  Scincns  ocellatus. 
Pyloric  extremity  of  the  slightly  marked  gastric 
dilatation  presents  an  angular  bend.     (Nuhn.) 


INTESTINE 


XSOPHAGUS 


Fig.   57. — Alimentary    canal    of 
Gohius  niger.     (Nuhn.) 


Fig.  55. — Series  of  sections  showing  human 
pyloric  valve  and  gastro-duodenal  junction  : 

1.  Stomach  of  foetus  at  term  in  section. 

2.  Adult  pyloric  valve,  ga.stric  surface. 

3.  Adult  pyloric  valve  and  gastro-duodenal 
junction  in  section. 

4.  Fcetal  gastro-duodenal  junction  in  section. 
Entrance  of  biliary  and  pancreatic  ducts  on 
summit  of  papilla  of  duodenum.  (Columbia 
University  Museum,  No.  1S51.) 


PYLORUS 


OESOPHAGUS 


Fig.  5S. — Alimentary  canal  of  shark.    (Nuhn.) 


PLATE    XXIV. 


DUODENUM 


XSOPHAGUS 


Fig.  59.— Stomacli  of  Phocavitulina,  harbor  seal. 
(Columbia  University  Museum,  No.  GOO.) 


DUODENUM 


OESOPHAGUS 


CARDIAC    END 
OF    STOMACH 


Fig.  60.— Stomach   of  PseHilenu/s  elegau.%  pond   turtle.      (Columbia  University 
Museum,  No.  1710.) 


ANATOMY.  41 

Th6  appearance  of  this  dilatation  marks  the  separation  of  the 
proximal  cephalic  part  (pharynx  and  oesophagus)  from  the 
distal  caudal  (intestinal)  portion  of  the  primitive  alimentary 
canal. 

Further  growth  of  the  stomach  takes  place  chiefly  along  the 
dorsal  margin  of  the  dilatation,  rendering  the  same  more  convex. 
The  ventral  border  develops  to  a  less  degree  and  in  the  course  of 
further  and  more  complete  differentiation  the  dorsal  margin  of 
the  future  stomach  assumes  even  at  this  period  the  character  of 
the  greater  curvature,  while  the  opposite  ventral  margin,  the 
future  lesser  curvature,  following  the  dilatation  of  the  tube  dor- 
sad, becomes  in  turn  concave  (Fig.  44,  6^). 

The  early  spindle-shaped  dilatation  has  therefore  assumed  the 
general  shape  of  the  adult  organ.  This  differentiation  of  greater 
and  lesser  curvature  begins  to  appear  in  embryos  of  5  mm.  (Fig. 
46)  and  is  very  well  marked  in  embryos  of  12.5  mm.,  Fig.  36,  of 
an  embryo  of  five  weeks,  indicates  the  adult  form  of  the  stomach 
clearly. 

It  will,  however,  be  noted  that  the  oesophageal  entrance  is  still 
at  the  cephalic  extremity  of  the  rudimentary  stomach,  while 
the  pyloric  transition  to  the  intestine  occupies  the  distal  caudal 
point,  under  cover  of  the  liver,  and  turns  with  a  slight  bend 
dorsad  and  to  the  right  to  pass  into  the  duodenum.  The  future 
greater  curvature  is  directed  dorsad  and  a  little  to  the  left  toward 
the  vertebral  column,  while  the  concave  lesser  curvature  is 
turned  ventrad  and  a  little  to  the  right  toward  the  ventral  abdom- 
inal wall.  At  this  time  there  is  but  little  indication  of  the 
subsequent  extension  of  the  organ  to  the  left  of  the  oesophageal 
entrance  to  form  the  great  cul-de-sac  or  fundus  of  the  adult 
stomach. 

In  this  stage  of  its  development  the  stomach  therefore  presents 
ventral  and  dorsal  borders,  and  right  and  left  surfaces,  while  the 
continuity  of  its  lumen  with  the  adjacent  segments  of  the  alimen- 
tary canal  appears  as  a  proximal  or  cephalic  oesophageal  and  a 
distal  or  caudal  intestinal  opening. 


42  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

COMPARATIVE   ANATOMY   OF    FOREGUT  AND   STOMACH. 

A  serial  review  of  this  portion  of  the  ahmentary  tract  in  verte- 
brates forms  one  of  the  most  interesting  and  instructive  chapters 
in  comparative  anatomy. 

Not  only  is  every  embryonal  stage  in  the  development  of  the 
higher  mammalia  represented  permanently  in  the  adult  structure 
of  some  of  the  lower  types,  but  the  far-reaching  influence  of  func- 
tion and  of  the  physiological  demands  on  the  structure  of  this 
portion  of  the  digestive  tract  is  strikingly  illustrated  by  the  numer- 
ous and  marked  modifications  which  are  encountered. 

The  foregut,  strictly  speaking,  is  in  mammals  separated  from 
the  oral  cavity  by  the  musculo-membranous  fold  of  the  soft  palate 
and  uvula.  In  all  other  vertebrates  except  the  crocodile,  the  oral 
cavity  and  foregut  pass  into  each  other  without  sharp  demarca- 
tion (Fig.  47).  In  some  of  the  lower  vertebrates  the  alimentary 
canal  never  advances  beyond  the  condition  of  a  simple  straight 
tube  of  nearly  uniform  caliber.  There  is  no  gastric  dilatation  and 
hence  no  differentiation  of  a  stomach  properly  speaking.  Such 
for  example  is  the  case  in  some  teleost  fishes,  as  the  pickerel 
(Fig.  48).  In  these  forms  we  have  to  deal  with  the  persist- 
ence of  the  early  embryonic  pregastric  stage  of  the  higher  types, 
before  the  simple  alimentary  tube  is  differentiated  by  the  appear- 
ance of  the  distinct  gastric  dilatation.    . 

In  the  Cydostomata  (Fig.  43)  the  intestinal  canal  passes  through 
the  body  in  a  perfectly  straight  line  and  the  three  segments  (mid-, 
fore-  and  hindgut)  are  not  clearly  differentiated. 

In  the  Ammocostes  the  foregut  begins  behind  the  wide  branchial 
basket,  dorsad  of  the  heart,  with  a  narrow  entrance,  which  is  suc- 
ceeded by  a  dilated  segment.  The  entrance  of  the  hepatic  duct 
separates  fore-  and  midgut. 

In  Amphioxus  the  branchial  pouch  passes  with  a  slight  constric- 
tion directly  into  the  gut  which  extends  through  the  body-cavity 
in  a  straight  Hne. 

The  narrow  segment  is  usually  regarded  as  the  "oesophagus." 
This  is  followed  by  a  slightly  dilated  segment,  the  "  stomach," 


STOMACH.  43 

into  which  a  blind  pouch  enters.     This  csecal  pouch  is  usually 
considered  as  a  hepatic  diverticulum  (Fig.  49). 

But  even  in  these  rudimentary  forms  the  point  where  the  liver 
develops  from  the  entodermal  intestinal  tube  marks  the  separa- 
tion of  fore-  and  midgut.  The  stomach,  when  it  develops,  is  situ- 
ated cephalad  of  the  entrance  of  the  hepatic  duct  into  the  intes- 
tine. The  section  cephalad  of  the  duct  opening  may  be  very 
short,  and  the  food  digested  further  on  in  the  intestinal  tube. 
Consequently  a  function  which  in  these  lower  vertebrates  is  as- 
signed to  the  midgut  becomes  transferred  in  the  higher  forms  to 
a  specialized  segment  of  the  foregut,  situated  cephalad  of  the 
hepato-enteric  duct.     This  segment  is  the 

STOMACH. 

The  distribution  of  the  vagus  nerve  finds  its  explanation  in  this 
derivation  of  the  stomach.  The  primitive  foregut  is  formed  by 
the  passage  between  the  branchial  cavity  and  the  midgut,  and  is 
within  the  area  supplied  by  the  vagus.  Hence  when  the  stomach 
develops  from  the  foregut,  as  a  specialized  segment  of  the  same,  it 
is  supplied  by  vagus  branches.  The  vertebrate  stomach  varies 
greatly  in  size  and  shape. 

The  type-form  is  presented  by  a  longitudinal  spindle-shaped 
dilatation  of  the  foregut,  which  retains  its  foetal  vertical  position 
in  the  long  axis  of  the  body.  An  example  of  this  form,  which  is 
encountered  among  fishes  and  amphibia,  is  presented  by  the  ali- 
mentary tube  of  Proteus  anguineus  and  Necturus  maculatus 
(Figs.  50  and  51).  Since  this  condition  is  common  to  all  verte- 
brates in  the  earliest  foetal  period  it  can  be  designated  as  the  foetal 
or  primitive  stomach  form.  All  others  appear  as  secondary  de- 
rivatives from  this  typical  early  condition. 

The  influences  which  bring  about  such  derivations  and  modi- 
fications may  be  enumerated  as  follows : 

1.  The  habitual  amount  of  food  required  by  the  animal. 

2.  The  volume  and  digestible  character  of  the  food. 

3.  The  size  and  shape  of  the  abdominal  cavity  in  which  the 
stomach  is  contained. 


44  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

4.  Structural  modifications  designed  to  increase  the  action  of 
the  gastric  juice  on  the  food  contained  in  the  stomach. 

5.  The  assumption,  on  part  of  the  stomach,  of  functions  which 
are  usually  relegated  to  other  organs. 

Most  of  the  individual  stomach  forms  encountered  among  ver- 
tebrates owe  their  production  to  several  of  these  influences  acting 
in  conjunction. 

We  may  group  the  main  types  as  follows  : 

1.  Stomach  Forms  Depending  on  the  Inflnence  exerted  by  the 
Habitual  Amount  of  Food  required  by  the  Animal. — The  greater  the 
activity  of  tissue  changes  is,  the  greater  will  be  the  amount  of 
food  required  and  the  more  pronounced  will  be  the  gastric  dila- 
tation of  the  alimentary  canal.  Hence  in  the  higher  vertebrates 
generally  the  stomach  appears  as  a  large  and  more  sac-like  dilata- 
tion than  in  lower  forms,  such  as  fishes  and  amphibia  and  some 
reptilia,  in  which  the  stomach  is  usually  smaller  and  foetal  in 
shape,  forming  a  slight  longitudinal  dilatation  situated  in  the  long 
axis  of  the  body.  An  example  is  seen  in  the  stomach  of  Coluber 
natrix  (Fig.  62).  Frequently  this  slight  dilatation  is  scarcely 
differentiated  from  the  oesophagus  at  the  cephalic  and  from  the 
small  intestine  at  the  caudal  end.  Many  batrachians  and  peren- 
nibranchiates  possess  this  form  among  the  amphibia.  It  is  also 
encountered  in  the  pickerels,  the  Cyprini,  and  in  Labrus  among 
fishes,  and  in  some  saurians  and  ophidia  among  reptiles.  It  con- 
stitutes a  slight  advance  in  development  over  the  earliest  stage 
represented,  as  we  have  seen,  by  the  nearly  uniform  and  undif- 
ferentiated alimentary  tube  of  amphioxus  and  the  cyclostomata. 

This  transition  of  the  foetal  form  to  the  more  advanced  secon- 
dary types  of  the  stomach  is  marked  by  the  development  of  two 
improtant  structural  features : 

(a)  The  separation  in  the  interior  of  the  canal  of  the  stomach 
from  the  intestine  by  the  appearance  of  a  ring-shaped  valve,  the 
pyloric  valve.  This  is  produced  by  an  aggregation  of  the  circular 
muscular  fibers  of  the  intestine  at  this  point,  and  causes  a  projec- 
tion of  the  mucous  membrane  into  the  lumen  of  the  canal.     It 


STOMACH  FORMS.  45 

begins  to  appear  in  the  fishes  (pickerel,  sturgeon,  etc.),  is  found 
in  most  amphibia  and  is  regularly  present  in  the  stomach  of  the 
higher  vertebrates.  (Figs.  54  and  65.)  A  good  example  of  the 
ring-shaped  plate  of  the  pylorus  with  central  circular  opening 
produced  by  the  aggregation  of  the  circular  muscular  fibers  is  af- 
forded by  the  view  of  the  interior  of  the  cormorant's  stomach  given 
in  Fig.  69.  The  opposite  or  oesophageal  extremity  of  the  stomach 
is  less  well  differentiated  from  the  afferent  tube  of  the  oesophagus. 

There  is  no  aggregation  of  muscular  circular  fibers  in  this  situa- 
tion and  no  valve.  Superficially  the  external  longitudinal  mus- 
cular fibers  of  the  oesophagus  pass  continuously  and  without 
demarcation  into  the  superficial  gastric  muscular  layer.  The 
separation  between  oesophagus  and  stomach  is,  however,  marked 
on  the  mucous  surface  by  a  well-defined  line  along  which  the  flat, 
smooth  and  glistening  oesophageal  tesselated  epithelium  passes 
into  the  granular  cuboidal  epithelium  of  the  gastric  mucous 
membrane.  The  oesophageo-gastric  junction  in  the  adult  human 
subject  is  shown  in  Fig.  53. 

(b)  The  pyloric  end  of  the  stomach  makes  an  angular  bend, 
while  the  rest  of  the  organ  remains  in  the  original  vertical  posi- 
tion in  the  long  axis  of  the  body.  An  example  of  this  condition 
is  presented  by  the  stomach  of  Sdncus  ocellatus  (Fig.  56  ;  cf  also 
Fig.  202). 

The  purpose  of  both  of  these  provisions  is  to  retain  the  gastric 
contents  for  a  longer  time  within  the  stomach.  Hence  this  form 
is  encountered  especially  in  those  fishes  and  amphibians  in  which 
the  nutritive  demands  require  a  more  complete  digestion  of  the 
food  taken.  This  is  the  case,  for  example,  in  Gobius  (Fig.  57), 
the  plagiostomata  (Fig.  58),  and  many  saurians.  The  same  transi- 
tory stomach  form  is  even  found  in  some  mammals,  as  the  seals. 
Fig.  59  shows  the  stomach  in  Phoca  vitulina,  the  harbor  seal. 
With  the  further  increase  in  the  demand  for  complete  digestion  of 
the  food  the  entire  stomach  assumes  a  transverse  position  to  the 
long  axis  of  the  body.  This  may  occur  while  the  stomach  still 
retains  its  primitive  tubular  form,  as  in  most  chelonians  (Fig. 


46  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

60).  In  others  the  change  in  position  occurs  after  the  gastric 
dilatation  has  assumed  the  sac-Hke  form,  as  in  many  land-turtles, 
crocodiles,  some  batrachians  and  all  higher  vertebrates  (Figs.  61 
and  62).  This  transverse  position,  at  right  angles  to  the  long  axis 
of  the  body,  forms  the  starting  point  for  the  derivation  of  all 
secondary  types  of  stomach. 

2.  Stomach  Forms  Depending  on  the  Influence  Exerted  by  the 
Volume  and  Digestible  Character  of  the  Foods. — Vegetable  sub- 
stances usually  have  a  large  volume  in  proportion  to  the  amount 
of  nutritive  material  which  they  contain.  Meat,  on  the  other 
hand,  contains  considerable  nutriment  in  a  comparatively  small 
bulk.  Hence  carnivora  (Fig.  63)  usually  have  a  smaller  stomach 
than  herbivora  (Fig.  64). 

3.  Stomach  Forms  Influenced  by  Size  and  Shape  of  the  Abdominal 
Cavity  in  which  they  are  Contained. — In  animals  whose  bodies  are 
long  and  slender,  as  in  snakes  (Fig.  52),  most  saurians  (Fig.  56), 
many  tailed  batrachians  and  perennibranchiates  (Figs.  50  and  51), 
many  teleosts  (Fig.  48),  the  stomach  is  likewise  usually  long  and 
slender  in  shape,  unless  special  modifying  conditions  exist.  When 
on  the  other  hand  the  body  is  broad  and  short,  as  in  Lophius 
(Fig.  65),  Pipa  (Fig.  66),  and  most  higher  vertebrates,  the  stomach 
is  also  broader  and  more  sac-like. 

4.  Stomach  Forms  Depending  on  Structural  Modifications  Designed 
to  Increase  the  Action  of  the  Gastric  Juice  on  the  Food. — This  pur- 
pose is  accomplished  : 

(a)  By  increasing  the  source  of  supply  of  the  gastric  juice. 

(b)  By  increasing  the  length  of  time  during  which  the  food 
remains  in  the  stomach. 

(a)  The  source  of  supply  of  the  gastric  juice  is  increased  by 
adding  to  the  usual  gastric  glands  of  the  stomach  a  special  acces- 
sory glandular  compartment,  either  placed  at  the  cardia,  where 
the  oesophagus  enters,  as  in  Myoxus  or  Castor  (Fig.  67)  or  attached 
to  the  body  of  the  stomach  to  the  left  of  the  cardia,  as  in  the 
manatee  (Fig.  68).  The  first  arrangement  is  similar  to  the  uni- 
versal position  of  the  glandular  stomach  of  birds  (Fig.  69).     In 


STOMACH  FORMS.  4:1 

birds,  however,  the  glandular  proventriculus  is  the  only  source 
of  the  gastric  juice,  while  in  the  above-mentioned  mammalia 
(myoxus  and  beaver)  the  accessory  glandular  stomach  is  merely 
an  addition  to  the  supply  derived  from  the  usual  gastric  glands 
situated  in  the  body  of  the  organ. 

(6)  The  increase  of  the  length  of  time  during  which  the  food 
remains  in  the  stomach  subject  to  the  action  of  the  gastric  juice 
can  be  accomplished  in  one  of  several  ways. 

1.  The  stomach,  while  it  retains  its  general  tubular  form  in- 
creases considerably  in  length  and  assumes  the  shape  and  structure 
found  in  the  human  large  intestine.  It  is  partially  subdivided 
by  folds  projecting  into  the  interior  and  separating  compartments 
resembling  the  colic  cells  of  the  human  large  intestine.  The  time 
required  for  the  passage  of  food  through  the  stomach  is  thus  in- 
creased and  the  action  of  the  gastric  juice  is  prolonged  and  ren- 
dered more  intense. 

Such  modifications  of  the  structure  of  the  stomach  are  encoun- 
tered in  Semnopithecus  among  the  monkeys  and  in  the  kangaroo, 
among  marsupials  (Figs.  70  and  71). 

2.  The  same  purpose  is  accomplished  by  the  development  of 
diverticula  from  the  stomach,  in  which  the  food  is  retained  and 
acted  on  by  the  gastric  juice  for  longer  periods. 

The  herbivora,  omnivora  and  such  carnivora  as  live  on  animal 
food  difficult  of  digestion  furnish  examples  of  this  type  of  stomach. 
The  same  is  also  found  in  most  teleosts.  In  the  latter  the  caecal 
gastric  pouch  lies  in  the  long  axis  of  the  body,  opposite  the  entrance 
of  the  oesophagus.  A  marked  example  of  this  arrangement  is  seen 
in  the  stomach  of  the  eel,  Anguilla  anguilla  (Fig.  72). 

In  other  forms,  and  in  the  mammalia  especially,  the  blind  pouch 
is  developed  from  the  portion  of  the  stomach  lying  to  the  left  of 
the  oesophageal  entrance  at  the  cardia,  and  is  hence  placed  trans- 
versely to  the  long  axis  of  the  body. 

This  difference  in  the  position  of  the  cul-de-sac  is  explained  by 
the  small  transverse  measure  of  the  body  in  teleosts,  while  the 
greater  amount  of  available  space  in  the  abdominal  cavity  of 


48  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

mammalia  permits  of  the  transverse  position  of  the  entire  stomach 
and  of  the  development  of  the  diverticulum  from  its  left  ex- 
tremity. 

Most  mammals  have  only  a  single  pouch,  whose  size  varies 
with  the  digestibility  of  the  food  habitually  taken.  It  is  greater 
in  herbivora  (Figs.  64  and  73)  than  in  omnivora  and  carnivora 
(Figs.  74  and  75).  In  some  of  the  latter,  as  Latra  (Fig.  63),  the 
cul-de-sac  is  almost  wanting. 

In  some  forms,  as  the  pig,  the  left  extremity  of  the  stomach 
carries  a  csecal  appendix  with  a  spiral  valve  in  the  interior  sepa- 
rating its  lumen  from  the  general  gastric  cavity  (Fig.  78).  Others 
have  two  such  csecal  appendices  added  to  the  left  end  of  the 
stomach  (Peccary,  Fig.  79).  These  csecal  pouches  may  arise  from 
the  body  of  the  stomach,  instead  of  from  the  left  extremity.  An 
example  of  this  condition  is  furnished  by  the  American  manatee 
(Fig.  68). 

5.  Variations  in  the  Form  of  the  Stomach  Depending  upon  the 
Assumption  by  the  Stomach  of  Special  Functions,  which  are  Usually 
Relegated  to  other  Organs. — These  functions  are  the  following: 

(a)  Storage  of  food  in  special  receptacles  or  compartments  for 
subsequent  use. 

(b)  Mastication  of  the  food  is  in  some  animals  accomplished 
only  partly  or  not  at  all  in  the  mouth,  and  is  then  performed  in 
the  stomach.  A  portion  of  the  stomach  is  thus  converted  into  an 
apparatus  for  mastication. 

(c)  The  provisions  for  these  two  accessory  functions  may  be 
combined  in  the  same  stomach. 

(a)  Many  of  the  higher  vertebrates  possess  in  connection  with 
the  alimentary  tract  additional  reservoirs  for  the  storage  of  food 
until  used.  Such  reservoirs  are  found  in  mammals  and  birds 
connected  with  the  oral  cavity,  as  cheek-pouches,  or  with  the 
oesophagus,  such  as  the  crop  of  the  birds  (Fig.  88).  Fig.  80 
shows  the  development  of  the  cheek-pouches  in  one  of  the 
primates,  Macacus  nemestrinus. 

In  many  mammals  reservoirs  of  similar  import  are  added  di- 


PLATE    XXV. 


DUODENUM 


CE80PHAGUS 


Fig.  fil. — Stomach  of  Cheh/dm  serpentinu,  snapping  turtle.   (Colum- 
bia University  Museum,  No.  i852.) 


CESOPHAGUS  AT 
JUNCTION  WITH 
C  A  R  D  I  A  OF 
STOMACH 


STOMACH  - 


DUODENUM 


PYLORUS  WITH 
THICKENED  RING 
OF  CIRCULAR  MUS- 
CULAR   FIBRES 


Fig.  62. — Same  in  section. 


PLATE    XXVI. 


PYLORUS 


CESOPHAGUS 


CESOPHACUS 


Fig.  63. — Stomach  of  Lutra  vulgaris, 
otter.     (Nuhu.)  Fig.  64. — Stomach  of  Eqmis  cahallus,  horse.     (Nuhn.) 


PYLORIC    CiECA 


PYLORUS 


(ESOPHAGUS 


Fig.  65. — Stomach  o{  Lnphius piscatorhis,  angler.     (Nnhii.) 


OESOPHAGUS 


STOMACH 


Fig.  66. — Stomach  of  Pipa  rentcosa.     (Nuhu. 


CZSOPHAGUS 


PROVENTRICULUS 


FUNDUS    OF 
STOMACH 


Fig.  67.— Stomach  of  (usior  tihcr,  ))faver.     (Ntihii. 


PLATE    XXVII. 


OECAL  POUCHES  CON- 
NECTED WITH  STOM- 
ACH 


PYLORUS 

PYLORIC    PORTION    OF 
STOMACH         (dices 
TIVE     SEGMENT^ 


OESOPHAGUS 


PROVENTRIC- 
ULUS 


CARDIAC    POR- 
TION     OF 
STOMACH 


Fig.  68. — Stomach  of  Manatus  americanns,  manatee.     (Nuhn.) 


PROYENTRICULUS 
OR  GLANDULAR 
STOMACH 


DUODENUM 


PYLORUS         ANO 
PYLORIC    VALVE 


CESOPHAGUS 


VENTRICULUS 
OR  MUSCU- 
LAR STOM- 
ACH 


Fig.   (59. — Stomach  of  Phalacrocorax   dilophiis,    douhle-crested    cormorant ;   section. 
(Columbia   University   Museum,  No.  ifj^.) 


PLATE    XXVIII. 


CESOPHAGUS 


DIVERTICULUM 
OF    FUNDUS 


DUODENUM 


Fig.  70. — Stomach  of  Halmaturus  derhyanus,  rock  kangaroo.     (Colum- 
bia University  Museum,  No.  582.) 


INTERMEDIATE  GAS- 
TRIC SEGMENT  RE- 
SEMBLING HUMAN 
COLON  IN  STRUCT- 
URE 


SMOOTH-WALLED    PY- 
LORIC  SEGMENT 


SACCULATED 
DIVERTICULA 
OF    FUNDUS 


Fig.  71.— Stomach  of  Semnopithems  entellus,  enteUus  moukey.     (Columbia  University  Museum, 

^o.  tI §5.) 


X^ 

m 

M 

"" 

oil  1 

T 

STOMACH 


GASTRIC    DIWER 
TICULUM 


Fig.  72. — Alimentary  canal  of  Angiiilla  angniUa,  eel.    (Colum- 
bia University  Museum,  No.  1271.) 


PLATE    XXIX. 


CESOPHAGUS 
FUNDUS 


Fig.  73. — Stomach  of  Lepiis  cunmihis,  rabbit.     (Nuhn.) 


Fig.  74. — Stomach  of  Nasua  rufa,  coati.     (Nuhn.) 


(ESOPHAGUS 


Fig.  75. — Stomach  of  FeUs  Jeo,  lion.     (Nuhn.) 


DUODENUM 


t* — CESOPHAGUS 


Fig.  7G.— Stomach  of   E.n,. 
University  Museum,  No.  358.) 


o,    .v.,iv.ncan   porcupine.     (Columbia 


PLATE   XXX. 


(ESOPHAGUS 


Fig.  77. — Stomach  of  Cercopithecus  cephus,  moustache  mon- 
key.    (Columbia  University  Museum,  No.  158.) 


CESOPHAGUS 


CiCCAL   APPENDIX 
OF   FUNDUS 


Fig.  78. — Stomach  of  Sus  serofa,  pig.  The  fundus  of  the  stomach  car- 
ries a  csecal  appendage  separated  in  the  interior  by  a  spiral  fold  of  the 
mucous  membrane  from  the  gastric  cavity. 


DORSAL       C/ECAL 
POUCH    OF    FUN 
DUS 


STOMACH       - 


PYLORIC^ 

antrum' 


._ji^- 


CESOPHAGUS 


VENTRAL  CjECAU 
POUCH  OF  FUN- 
DUS 


Fig.  79. — Stomach  of  DicolyJes  forquatits,  peccary.  The  fundus  is  a  caiKK  imis  ikhkIi  prolonged 
ventrally  and  dorsally  into  two  caecal  appendages  resembling  the  single  appendage  of  the  pig's 
stomach.     (Columbia  University  Museum,  No.  1806.) 


PLATE    XXXI. 


BUCCAL  ORIFICE 
OF    POUCH 


Fig.  80. — Macnens  nemestrinns,  pig-tail  macaque  monkey ;  cheek-pouches.     (From 
fresh  dissection.) 


DUODENUM 
PYLORIC    SEGMENT 

(digestive  STO 

ACH    proper) 


OESOPHAGUS 

CARDIAC  PORTION 
OF  STOMACH  DE- 
VOID OF  GASTRIC 
GLANDS  AND 
FORMING  A  STOR- 
AGE   CHAMBER 


Fig.  81. — Stomach  of  Cricetus  vulgaris,  hamster.     (Nuhn.) 


PLATE    XXXII. 


CEOSPHAGUS 


RETICULUM 


PSALTERIUM 


ABOMASUS 


Fig.  82. — Stomach  of  Ovis  aries,  sheep.     (Columbia  University 
Museum,  No.  1807.) 


CESOPHAGUS 


3D   STOMACH 
(psalter  lUM' 


2d  stomach 
(reticulum) 
4th     stomach 
(abomasus      or 
digestive  stom- 
ACH proper) 


DUODENUM 


1st  stomach 

(rumen) 


Fig.  83. — Scheme  of  ruminant  compound  stomach.     (Nuhn. 


PLATE    XXXIII. 


Fig.  84. — Mucous  niembraue  of  stomach  of  Camelns  dioniedarius,  dromedary,  showing  •water- 
celts.     (Cohimbia  University  Museum,  No.  1123.) 


DUODENUM 


: — (XSOPHAGUS 


FiQ.  85. — Stomach  of  PAoca?Hfl,  porpoise.     (Xuhn.) 


PLATE    XXXIV. 


DUODENUM 


CESOPHAGUS 


PROVENTRICULUS 
OR  GLANDULAR 
STOMACH 


TENDON-PLATE  OF 
MUSCULAR  STOM- 
ACH 


MUSCULAR  STOM- 
ACH OR  VENTRIC- 
ULUS 


Fig.  86. — Stomach  of  I'rinatorimher,  red-throated  loon.  (Columbia  Uuiversity 
Museum,  No.  1808.) 


OESOPHAGUS 


OESOPHAGUS 


DUODENUM 


proventriculus 
(glandular   stom- 
ach) 


VENTRICULUS 
MUSCULAR  stom- 
ach) 


Fig.  87. — Scheme  of  stomach  of  grauivorous  bird.     (Nuhu.^ 


PLATE   XXXVI. 


DUODENUM 
PYLORUS 


MUSCULAR 
STOMACH 


;.  — CESOPHAGUS 


PROVEN- 
TRICULUS 


Fig.  90. — Stomach  of  owl  sp.     (Xuhu.) 


DUODENUM 


PY  LO  R I C 
STOMACH 


MUSCULAR 
STOMAC 


CESOPHAGUS 


PROVCNTRIC- 
ULUS 


Fig.  91. — Stomach  of  Ardea  cinerea,  herou.     (Xuhn.) 


PYLORUS 
DUODENUM 


PYLORIC 
STOMACH 


XSCPHAGUS 


MUSCULAR    STOM- 
ACH  WITH   TENDI- 
j         NOUS    CENTRE 


Fig.  92. — Stomach  of  crocodile.     (Nnhn.) 


IS 
i  '^ 

ci  6 

c5  a" 


PLATE    XXXVIII. 


(ESOPHAGUS 


PYLORUS 

OECAL  APPENDAGE 
WITH  LONGITUDI- 
NAL  MUCOUS 
FOLDS,  DEVOID  OF 
GASTRIC    GLANDS 

Fig.  95. — Stomach  of  Brady  pus  tridactylus,  three-toed  sloth. 

I.  First  stomach,  devoid  of  gastric  glands,  corresponding  to  rumen  of 
ruminants. 

II.  Second  stomach,  the  homologue  of  the  ruminant  reticulum. 

III.  Digestive  stomach  proper,  provided  with  gastric  glands  connected 
hy  a  gutter  with  the  oesophagus. 

IV.  Muscular  stomach,  the  walls  formed  by  a  thick  muscular  plate  and 
provided  on  the  mucous  surface  with  a  dense  corneous  covering  for  purposes 
of  trituration. 


/V*>> 


DUODENUM 


THICKENED  MUS- 
CULAR FIBRES 
OF  PYLORIC 
SEGMENT 


Fig.  96.— Stomach  of  Tmnantua  hirittata,  collared  ant-eater. 
(Columbia  University  Museum,  No.  xlis) 


PLATE   XXXIX. 


PRIMORDIAL 
CRANIUM 


UMBILICAL 
CORD 
CAUDAL   GUT- 
RENAL    BUD 


FORE-GUT 


BRANCHIAL   CLEFTS 


COMMON    DORSAL 
MESENTERY 

WOLFFIAN    BODY 


DUCT   OF 
ALLANTOIS 


Fig.  97. — Alimenfary  canal  of  liuman  embryo  of  5  mm.      X  15.     (Eeconstruction  after  His.) 


DUODENUM 


DESCENDING 
LIMB  OF  IN- 
T  E  ST  I  N  A  L 
LOOP 


VITELLO-INTES- 
TINAL    DUCT 


ASCENDING  LIMB 
OF  INTESTINAL 
LOOP 


Fig.  98. — Schema  of  human  embryonic  intestinal  canal,  with  intes- 
tinal umbilical  loop,  but  before  diflereutiation  of  the  large  and  small 
intestine. 


PLATE   XL, 


STOMACH 
SPLEEN 

VENTRAL    WESO- 
GASTRIUM 

PYLORUS 
PANCREAS 


TRUNCUS 
ARTERIOSUS 


OSTIUM     OF 

OVIDUCT 
LEFT    LUNG 


LEFT   OVIDUCT 


DORSAL    MESO- 
GASTRIUM 


LEFT    OVARY 


-  INTESTINE 


Fig.  99. — Viscera  of  yectuncs  macidatiis,  mud-puppy,  in  situ.     (Columbia  University  Museum, 
No.  1175.) 


STOMACH  FORMS.  49 

rectly  to  the  stomach  and  form  an  integral  part  of  the  organ. 
Examples  are  furnished  by  the  compound  stomachs  of  many 
rodents,  ruminants,  cetaceans  and  herbivorous  edentates.  The 
peculiar  appearance  of  these  stomachs  is  explained  if  the  addi- 
tional reservoirs  are  in  imagination  removed  and  the  digestive 
stomach  proper  restored  so  to  speak  to  the  type-form.  The  prox- 
imal or  cardiac  portion  of  the  stomach  in  many  rodents  is  devoid 
of  gastric  glands  and  must  be  interpreted  as  a  storage  chamber 
for  food  (Fig.  81).  The  same  significance  attaches  to  the  corre- 
sponding portion  of  the  manatee's  stomach  (Fig.  68). 

Similar  contrivances  are  found  in  the  ruminant  stomach.  The 
first  and  second  divisions  (rumen  and  reticulum)  are  nothing  but 
sac-like  gastric  reservoirs  or  pouches,  in  which  the  food  is  col- 
lected, to  be  subsequently  returned  to  the  mouth  for  mastication. 
When  swallowed  for  the  second  time  the  bolus  is  carried,  by  the 
closure  of  the  so-called  oesophageal  gutter,  past  the  first  and  sec- 
ond stomach  into  the  digestive  apparatus  proper  (the  abomasum) 
(Figs.  82  and  83).  Many  ruminants  (e.  g.,  Moschus)  only  have 
these  three  compartments.  Most,  however,  have  four,  the  leaf 
stomach  or  psalterium  being  intercalated  between  the  retinaculum 
and  the  abomasum.  The  psalterium  contains  no  digestive  glands. 
It  may  possibly  serve  for  the  absorption  of  the  liquid  portions  of 
the  foods. 

The  rumen  or  first  stomach  of  the  camels  and  llamas  is  provided 
with  so-called  "  water-cells,"  for  the  storage  of  water.  These  cells 
are  diverticula  lined  by  a  continuation  of  the  gastric  mucous 
membrane.  The  entrance  into  these  compartments  can  be  closed 
by  a  sphincter  muscle  after  they  are  filled  with  water  (Fig.  84). 

The  three  stomachs  of  the  cetaceans  are  similar  to  those  of  the 
ruminants  (Fig.  85).  The  first  is  a  crop-like  reservoir  for  the  re- 
ception of  the  food  when  swallowed.  The  mucous  membrane  is 
entirely  devoid  of  digestive  glands.  In  the  dolphins  the  mucous 
membrane  is  provided  with  a  hard  horny  covering,  which  serves 
to  break  up  the  food  mechanically  by  trituration.  The  second 
stomach  and  the  gut-like  pyloric  prolongation  constituting  the 
4 


50  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

third  stomach  contain  gastric  glands  and  are  hence  digestive  in 
function. 

(b)  Stomach  forms,  in  which  a  portion  of  the  organ  is  converted 
into  an  apparatus  for  mastication,  are  seen  especially  in  birds,  in 
which  animals,  on  account  of  the  absence  of  teeth,  mastication 
cannot  be  performed  in  the  mouth. 

The  stomach  of  the  bird  is  usually  composed  of  two  segments, 
one  placed  vertically  above  the  other. 

The  first  appears  like  an  elongated  dilatation  of  the  oesophagus, 
forming  the  Froventriculus  or  glandular  stomach. 

The  second  is  larger,  round  in  shape,  with  very  strong  and  thick 
muscular  walls  (Figs.  86  and  87). 

The  proventriculus  furnishes  the  gastric  juice  exclusively. 

The  second  or  muscular  stomach,  devoid  of  gastric  glands,  func- 
tions merely  as  a  masticating  apparatus  for  the  mechanical  division 
of  the  food.  The  thick  muscular  walls  of  this  compartment  may 
measure  several  inches  in  diameter  and  carry  on  the  opposed  mu- 
cous surfaces  lining  the  cavity  a  hard  horny  plate  with  corrugated 
and  roughened  surface  (Fig.  88).  These  hard  plates  are  designed 
to  crush  the  food  between  them,  as  between  two  mill  stones. 
The  muscle  stomach  is  best  developed  in  herbivorous  birds,  while 
both  the  muscular  wall  and  the  horny  plate  are  much  weaker 
and  thinner  in  carnivore  wading  and  swimming  birds  (Fig. 
89). 

In  birds  of  prey,  especially  in  the  owls,  the  stomach  walls  are 
scarcely  more  massive  than  in  other  animals,  and  the  mucous 
membrane  is  soft  and  devoid  of  a  horny  covering.  The  glandular 
and  masticatory  stomachs  are  less  sharply  divided  from  each  other 
in  these  forms,  and  the  entire  organ  conforms  more  to  the  general 
vertebrate  type  (Fig.  90). 

In  some  birds  (herons,  storks,  etc.)  a  small  rounded  third 
stomach,  the  so-called  pyloric  stomach,  is  placed  between  the 
muscle  stomach  and  the  pylorus  (Fig.  91).  It  contains  no  gastric 
glands,  and  possibly  may  function  as  an  additional  absorbing 
chamber. 


INTESTINE.  51 

Among  reptiles  the  stomach  of  the  crocodile  resembles  the  organ 
in  birds  (Fig.  92).  It  is  flat  and  rounded  in  shape,  the  muscle  wall 
carries  a  tendinous  plate,  and  there  is  a  pyloric  stomach.  There 
is,  however,  no  glandular  stomach  or  proventriculus,  as  in  birds, 
and  the  mucous  membrane  is  not  covered  by  a  horny  plate,  but 
is  soft  and  contains  the  peptic  glands.  Figs.  93  and  94  show  the 
stomach  of  Alligator  mississippiensis,  in  the  ventral  view  and  in 
section. 

(c)  The  combination  of  the  two  accessory  functions  just  described 
in  the  same  stomach  is  found  in  the  three-toed  sloth  (Fig.  95). 

There  are  here  two  large  reservoirs,  which  correspond  to  the 
rumen  and  retinaculum  of  the  ruminants,  and  a  digestive  com- 
partment containing  gastric  glands,  which  corresponds  to  the 
ruminant  abomasum,  and  is  connected  by  an  oesophageal  gutter 
directly  with  the  oesophagus.  At  the  pyloric  extremity  the  muscle 
wall  is  greatly  increased  and  the  mucous  membrane  of  this  portion 
carries  a  thick  horny  covering,  forming  a  masticatory  stomach 
greatly  resembling  the  corresponding  structure  in  the  bird.  Its 
function  is  evidently  to  complete  the  mechanical  division  of  the 
food  which  has  only  been  partly  masticated  in  the  mouth. 

The  same  significance  is  probably  to  be  attached  to  the  thickened 
muscular  walls  which  the  pyloric  segment  of  the  stomach  in 
Tamandua  bivittata,  another  edentate,  presents  (Fig.  96),  in  strong 
contrast  with  the  thinner  walled  cardiac  segment  and  fundus. 

INTESTINE. 

Continuing  our  consideration  of  the  development  of  the  ali- 
mentary canal  we  find  that  changes  from  the  simple  primitive 
straight  tube  below  the  stomach  depend  upon  two  factors : 

1.  The  increase  in  the  length  of  the  intestinal  tube,  which  ex- 
ceeds relatively  the  increase  in  the  length  of  the  body  cavity  in 
which  it  is  contained. 

2.  The  differentiation  into  small  and  large  intestine,  the  devel- 
opment of  the  caecum  and  ileo-csecal  junction,  and  the  development 
of  the  accessory  digestive  glands,  liver  and  pancreas,  by  budding 


52  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

from  the  proximal  portion  of  the  primitive  entodermal  intestinal 
tube. 

1.  In  embryos  up  to  5  mm.  cervico-coccygeal  measure  (Fig. 
97)  the  intestinal  tube  follows  the  body  curve  without  devia- 
tion. Subsequently  the  elongation  of  the  intestine  causes  a 
small  bend,  with  the  convexity  directed  ventrad,  to  appear  in 
the  umbilical  region.  This  bend  gradually  increases  until  the 
gut  forms  a  single  long  loop,  beginning  a  short  distance  below  the 
pylorus  and  directed  ventro-caudad.  The  apex  of  the  loop,  to 
which  the  vitello-intestinal  duct  is  attached  (Fig.  98)  (cf  p.  34) 
projects  beyond  the  abdominal  cavity  into  the  hollow  of  the 
umbilical  cord,  constituting  the  so-called  "  umbilical  or  embryonal 
intestinal  hernia."  This  entrance  of  the  apex  of  the  intestinal 
umbilical  loop  into  the  umbilical  cord  begins  in  embryos  of  about 
10  mm.  During  the  succeeding  weeks — up  to  the  tenth — the 
segment  of  the  intestine  thus  lodged  within  the  hollow  of  the 
umbilical  cord  increases.  After  this  period  the  intestinal  coils 
are  gradually  withdrawn  within  the  abdomen.  The  explanation 
of  this  temporary  extrusion  of  the  intestine  into  the  umbilical 
cord  is  probably  to  be  found  in  the  strain  produced  by  the  yolk- 
sac  which  is  attached  by  the  vitello-intestinal  duct  to  the  apex  of 
the  umbilical  loop.  As  we  have  seen  (p.  35)  the  site  of  the 
original  apex  of  the  loop  may  still  be  indicated  in  the  adult  by 
the  persistence  of  a  portion  of  the  vitello-intestinal  duct  as  a 
"  Meckel's  diverticulum." 

In  its  simplest  primitive  condition  the  loop  presents  a  proximal, 
descending  or  efferent  limb,  an  apex,  and  an  ascending,  returning 
or  afferent  limb  (Fig.  98).  In  the  human  embryo  these  segments 
of  the  loop  furnish  the  jejuno-ileum  and  portions  of  the  large 
intestine,  in  a  manner  to  be  subsequently  detailed. 

This  stage  in  the  development  of  the  higher  vertebrate  intestine 
is  well  illustrated  by  the  alimentary  tract  of  the  mud-puppy,  Nec- 
turus  maculatus,  shown  in  Fig.  99,  which  represents  the  entire 
situs  viscerum  of  an  adult  female  animal. 

The  stomach  is  tubular,  not  distinctly  differentiated  from  the 


DIFFERENTIATION  OF  INTESTINES.  53 

oesophagus,  placed  vertically  in  the  long  axis  of  the  body.  The 
pyloric  end  is  marked  by  a  constriction  separating  stomach  from 
midgut  and  immediately  beyond  this  point  the  pancreas  is  ap- 
plied to  the  intestine.  The  rest  of  the  intestinal  canal  forms  a 
simple  loop,  the  descending  limb  presenting  one  or  two  primitive 
convolutions.  There  is  no  marked  differentiation  between  large 
and  small  intestine,  the  canal  possessing  a  nearly  uniform  cahber 
from  pylorus  to  cloaca. 

2.  The  differentiation  of  the  small  from  the  large  intestine, 
marked  by  the  appearance  of  the  csecal  bud  or  protrusion  (Fig. 
100),  takes  place  in  the  ascending  segment  of  the  umbilical  loop 
a  short  distance  from  the  apex.  In  the  human  embryo  the 
csecal  bud  appears  in  the  6th  week  as  a  plainly  marked  pro- 
tuberance, which  grows  very  slowly  in  length  and  circumfer- 
ence. It  shows  very  early  an  unequal  rate  of  development ;  the 
terminal  piece,  not  keeping  pace  in  growth  with  the  proximal 
portion,  is  converted  into  the  vermiform  appendix,  while  the 
proximal  segment  develops  into  the  caecum  proper.  The 
increase  in  the  length  of  the  loop,  which  begins  to  be  marked 
in  the  7th  week,  is  not  uniform.  The  apex  is  the  first  portion  to 
present  the  evidences  of  this  growth.  Subsequently  the  descend- 
ing limb  grows  in  length  very  rapidly  and  is  early  thrown  into 
numerous  coils  of  the  future  mobile  portion  of  the  small  intestine 
(jejuno-ileum).  Even  before  the  withdrawal  of  the  apex  of  the 
loop  within  the  abdominal  cavity  a  prominent  coil  of  these  con- 
volutions is  found  protruding  in  the  umbilical  region  (Fig.  544) 
The  ascending  limb  of  the  loop  from  which  a  portion  of  the  large 
intestine  is  developed,  grows  comparatively  slowly  at  this  time. 

The  future  portions  of  the  human  adult  alimentary  tract  below 
the  stomach  may  be  referred,  in  reference  to  their  derivation,  to 
this  primitive  condition  of  the  tube  as  follows  : 

1.  The  segment  of  small  intestine  situated  between  the  pylorus 
and  the  beginning  or  point  of  departure  of  the  proximal  or  de- 
scending limb  of  the  umbilical  loop,  develops  into  the  duodenum. 
This  portion  of  the  small  intestine  is  indicated  early  in  embryos 


54  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

of  2.15  mm.  (Fig.  101),  by  the  origin  of  the  hepatic  duct  from 
the  intestinal  tube.  Somewhat  later,  in  embryos  of  4.10-5  mm. 
length,  (Fig.  102)  it  becomes  additionally  marked  by  the  origin 
of  the  pancreatic  diverticulum.  The  duodenum,  at  first  straight, 
now  begins  to  curve,  forming  a  short  duodenal  loop  or  bend.  In 
embryos  of  6  weeks  the  duodenum  forms  a  simple  loop  placed 
transversely  below  the  pyloric  extremity  of  the  stomach  (Figs. 
103  and  104). 

2.  The  descending  limb,  the  apex  and  a  small  part  of  the  as- 
cending limb  of  the  umbilical  loop  form  the  jejuno-ileum. 

3.  The  remainder  of  the  ascending  limb  forms  the  caecum  and 
appendix,  the  ascending  and  transverse  colon. 

4.  The  distal  straight  portion  of  the  primitive  tube  forms  the 
terminal  portion  of  the  transverse  colon  (the  splenic  flexure),  the 
descending  colon,  sigmoid  flexure  and  rectum. 

The  primitive  condition  of  the  embryonal  mammalian  alimen- 
tary tract,  after  difierentiation  of  the  large  intestine  is  well  illus- 
trated by  some  of  the  lower  vertebrates  in  which  development 
never  proceeds  beyond  this  stage.  Fig.  112  shows  the  entire  ali- 
mentary canal  of  a  teleost  fish,  the  conger  eel  {Echelus  conger) 
isolated. 

The  preparation  forms  a  good  illustration  of  the  embryonal 
stage  of  the  higher  vertebrates  in  which  development  has  not 
proceeded  beyond  the  formation  of  the  simple  umbilical  loop, 
about  corresponding  to  the  schematic  Fig.  98.  The  stomach  is 
difierentiated  both  by  its  caliber  and  by  the  formation  of  a 
pyloric  ring  valve. 

The  midgut  forms  a  simple  loop  with  a  descending  and  ascend- 
ing limb  closely  bound  together  by  mesenteric  attachment.  Dif- 
ferent from  the  course  of  development  followed  in  the  human 
embryo  is  the  situation  of  the  ileo-colic  junction.  The  same  ap- 
pears in  the  terminal  straight  segment  of  the  canal — correspond- 
ing to  the  human  descending  colon — while  in  the  human  embryo 
the  difierentiation  of  small  and  large  intestine  takes  place  in  the 
course  of  the  ascending  limb  of  the  loop.     This  condition  de- 


PRIMITIVE  TYPES.  55 

pends  upon  the  relatively  much  shorter  extent  of  the  teleost 
endgut  compared  with  the  human  large  intestine.  Other  ex- 
amples are  afforded  by  the  alimentary  tract  of  some  of  the 
Amphibia  and  Reptilia.  Fig.  105  shows  the  alimentary  canal 
of  Rana  catesbiana,  the  common  bull  frog.  The  stomach,  fairly 
well  differentiated,  is  succeeded  by  the  small  intestine  of  consid- 
erable length  and  uniform  caliber.  The  proximal  portion  of  the 
small  intestine  is  characterized  as  duodenum  by  its  connection 
with  liver  and  pancreas.  In  the  remaining  portion  of  the  intes- 
tinal canal  it  is  not  difficult  to  recognize  the  elements  of  the 
umbilical  loop  of  the  higher  mammalian  embryo.  The  larger 
mass  of  the  jejuno-ileal  coils  is  developed  from  the  descending 
limb  of  the  loop ;  a  smaller  number  of  convolutions  belong  to  the 
returning  or  ascending  limb,  which  also  includes  the  ileo-colic 
junction.  The  very  short  large  intestine  of  the  frog  passes  straight 
down  to  enter  the  cloaca.  Another  example,  in  which  the  early 
embryonal  stages  of  the  higher  mammalia  are  illustrated  by  the 
permanent  structure  of  one  of  the  lower  vertebrates,  is  given  in 
Fig.  106,  which  shows  the  alimentary  tract  of  a  chelonian,  Pseu- 
demys  elegans,  the  pond  turtle.  The  bilobed  liver  fits  over  the 
well-differentiated  stomach  in  the  manner  of  a  saddle.  The 
stomach  itself,  as  in  chelonians  generally,  has  a  markedly  trans- 
verse position  and  passes  under  cover  of  the  right  lobe  of  the 
liver  into  the  duodenum.  The  coils  of  small  intestine  form  a 
prominent  mass,  which,  however,  when  unravelled  as  shown  in 
the  figure,  permits  us  to  recognize  its  identity  with  the  mamma- 
lian embryonic  umbilical  loop.  The  well-marked  ileo-colic  junc- 
tion is  situated  at  the  termination  of  the  returning  limb  of  the 
loop,  close  to  the  beginning  of  the  descending  limb.  This  close 
approximation  of  the  duodenum  and  colon  (duodeno-colic  isth- 
mus) forms  one  of  the  most  important  factors  in  the  further 
development  of  the  mammalian  intestinal  canal  and  will  again 
be  referred  to  below. 

From  the  ileo-colic  junction  the  large  intestine  of  the  turtle  con- 
tinues caudad  to  the  cloaca  in  a  nearly  straight  line.     The  same 


56  ANAT03IY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

primitive  condition  of  the  intestinal  canal  may  be  observed  in 
some  members  of  man's  own  class,  the  mammalia — as  in  certain 
edentates.  Figs.  107  and  108  show  the  entire  abdominal  portion 
of  the  alimentary  tract  in  Tamandua  bivittata,  the  little  ant-eater 
of  Brazil.  The  stomach  is  turned  cephalad  and  the  great 
omentum  elevated.  The  intestines  are  turned  over  to  the  right 
side. 

It  will  be  observed  that  in  spite  of  the  numerous  coils  of  the 
small  intestine  the  general  arrangement  of  the  alimentary  canal 
corresponds  to  the  primitive  scheme  shown  in  Fig.  98.  The  entire 
intestinal  canal  is  attached  by  a  continuous  vertical  mesentery  to 
the  dorsal  median  line  of  the  abdominal  cavity  ventrad  of  the 
vertebral  column  and  aorta.  The  growth  in  length  of  the  small 
intestine  has  necessitated  a  corresponding  lengthening  of  the  at- 
tached border  of  the  mesentery — consequently  the  membrane 
presents  a  pleated  or  crenated  appearance.  The  csecum  is  well 
developed,  the  ileo-csecal  junction  being  situated  within  the  re- 
turning limb  of  the  loop,  a  little  distance  from  the  apex. 

In  Figs.  109  and  110,  taken  from  the  same  specimens,  the  en- 
tire mass  of  the  small  intestines  has  been  turned  to  the  left  so  as 
to  exhibit  the  right  leaf  of  the  common  dorsal  mesentery  and  the 
mesoduodenum,  the  latter  containing  the  head  of  the  pancreas.  It 
will  be  noted  that  the  mesentery,  expanding  beyond  the  duodeno- 
colic  isthmus,  is  common  to  the  small  and  to  the  proximal  por- 
tion of  the  large  intestine,  i.  e.,  to  those  segments  of  the  alimentary 
canal  which  are  developed  from  the  two  limbs  of  the  umbilical 
loop.  Figs.  107-110  should  be  studied  and  compared  together,  as 
each  supplements  the  others. 

It  will  be  observed,  in  reference  to  the  change  from  the  primi- 
tive loop  to  the  subsequent  increase  in  the  length  of  the  tube  and 
the  resulting  arrangement  of  the  mesentery,  that  three  successive 
stages  are  to  be  considered,  represented  schematically  in  Fig. 
111.  In  the  earliest  stage  (Fig.  Ill,  I.)  the  two  segments  of  the 
loop  are  of  equal  length,  parallel  to  one  another,  the  distance  be- 
tween the  beginning  and  termination  of  the  loop  (1-2)  being 


PLATE   XLI. 


(XSOPKAGUS 


JEJUNO-ILCUM  DE- 
VELOPED FROM 
DESCENDING 
LIMB  OF  INTES- 
TINAL   LOOP 


ORIGINAL   APEX 
OF     LOOP    (site 

of      meckel's 
diverticulum) 


DUODENUM 


SEGMENT  OF  ascend- 
ing LIMB  OF  LOOP 
FURNISHING  ASCEND- 
ING AND  TRANSVERSE 
COLON 

DESCENDING   COLON 


Fig.  100. — Schema  of  human  embryonic  intestinal  canal  after  diflfereutiation 
of  the  large  and  small  intestine. 


SEESSEL'S   SAC 


HEAD-GUT 


CAUDAL  GUT 


STALK    OF 
ALLANTOIS 


STOMADSUM 


HEPATIC    BUD 


YOLK-SAC 


—MID-GUT 


ENTRANCE    INTO 
HIND-GUT 


ALLANTOIC 
DUCT 


Fig.  101.— Human  embryo  of  2.15  mm.,  twelve  days  old.  Seessel's 
sac  is  the  cephalic  blind  termination  of  the  embryonic  fore-gut  before  the 
communication  with  the  ectodermal  invagination  of  the  stomadseum  has 
been  formed.     (Reconstruction  after  His.) 


PLATE    XLII. 


EPIGLOTTIS 


TONGUE 
HYPOPHYSIS 


VITELLINE    DUCT 


CAUDAL    END 

OF  VERTEBRAL. 

COLUMN 

ALLANTOIC 
DUCT 


CAUDAL   GUT 


LUNG    VESICLE 


STOIVIACH 


PANCREAS 


URINARY 
BLADDER 


WOLFFIAN 
DUCT 

RENAL   BUD 


Fig.  102.— Eepresentation  of  alimentary  canal  and  appendages  of  human  embryo 
of  4.1  mm. ;  isolated.     X  15.     (Kollmann,  after  His.) 


EPIGLOTTIS- 


HYPOPHYSIS 


HCAD-GUT 


INTESTINAL- 
LOOP 

ALLANTOIC 
DUCT 

GENITAL    PRO- 
TUBERANCE 
CAUDAL    END 
OF  VERTEBRAL 
COLUMN 


STOMACH 


PANCREAS 


WOLFFIAN 
DUCT 


URINARY 
BLADDER 
RENAL  BUD 


CAUDAL   GUT 


Fig.  103. — Alimentary  canal  and  appendages  of  human  em- 
bryo of  12.5  mm.     X  12.     (Kollmann,  after  His.) 


PLATE    XLIII. 


CESOPHAGUS 


DORSAL      MESOGASTRIUM 


VENTRAL    MESOGASTRIUM 

DUODENUM 

SUPERIOR    MESENTERIC 
ARTERY 

DUODENO-COLIC 
ISTHMUS 
ART.    COLICA    MEDIA 


JEJUNO-ILEUM 
C>ECUM 
INF      MESENTERIC    ART. 
VITELLINE    DUCT    AND 
OMPHALO  -  MESEN- 
TERIC   ART. 


Fk;.  104. — A.  Schematic  representation  of  alimentary 
canal,  with  umbilical  loop  and  mesenteric  attachments  in 
human  embryo  of  about  six  weeks.  B  and  C,  stages  in  the 
intestinal  rotation. 


PLATE    XLIV. 


I  LEO-COLIC 
JUNCTION 


(XSOPHAGUS 


STOMACH 


PANCREAS 


DUODENUM 


Fig.  105. — Bona  cafesMana,  hnll-frog.     Alimentary  canal  and  append- 
ages.    (Columbia  University  Museum,  No.  1454.) 


RIGHT   LOBE 
OF    LIVER 


(LEO-COLIC 
JUNCTION 


SMALL 
INTESTINE 


(ESOPHAGUS 


LEFT   LOBE 
OF    LIVER 


Fig.  106.— Pseudemys  elegans,  pond  turtle.   Alimentary  canal.    (Columbia  University  Museum. 
No.  1437.) 


PLATE    XLV. 


DUODENO 
COLIC  ISTH 
MUS 


i SaH  STOMACH 


PANCREAS 


TERMINAL 
BEND  OF 
COLON 


ILEO-COLIC 
JUNCTION 


Fig.  107.— Abdominal  viscera  of  Tamnmhia  birittata.  the  little  ant-eater,  seen  from  the  left, 
with  the  intestines  turned  to  the  right.     (From  a  fresh  dissection.) 


PLATE    XLVI. 


PYLORUS  — ^.-;-- 


DUODENO 
JEJUNAL 
TRANSI 
TION 


SMALL  IN- 
TESTINE 
FORMING 
EFFERENT 
LIMB  OF 
INTESTI- 
NAL LOOP 


tLEO-COLIC 
JUNCTION 


GREAT 
OMEN- 
TUM 
TURNED 
UP 


SUPERIOR 
M  E  S  E  N  - 
TERIC  AR- 
TERY IN 
DUODENO- 
COLIC 
ISTHMUS 

COLON  AT 
TERMINA- 
TION OF 
AFFERENT 
LIMB  OF 
INTEST  I  - 
NAL    LOOP 


COLON    : 
PROXIMAL 
SEGMENT 
FORMING 
AFFERENT 
LIMB    OF 
INTESTI- 
NAL LOOP 


Fig.  108.— The  same  view,  from  another  speeimeu. 
and  compared  together,  as  each  supplements  the  otlier. 


Figures  107  and  108  should  be  studied 


PLATE    XLVII. 


DUODE- 
NUM 


RIGHT 
KIDNEY 


BEND    OF 

COLON 

TURNING 

CAUDAD 

INTO 

SHORT 

TERMINAL 

PORTION 

OF    LARGE 

INTESTINE 


STOMACH 


DUODENO- 

COLIC 

ISTHMUS 


ILEO-COL1C 
JUNCTION 


Fig.  109. — Ahdomiiml  viscera  (if  TitnimuUia  hirittain,  the  little  ant-eater,  seen  from  the  right, 
with  the  intestines  turned  to  the  left.     (From  a  fresh  dissection.) 


PLATE    XLVIII. 


CAUDATE    LOBE 
OF    LIVER 
POST   CAVA 

PROBE    PASSED 

THROUGH 

FORAMEN       OF 

WINSLOW 


R.   KIDNEY 


COLON  TURN' 
ING    INTO 
TERMINAL 
SEGMENT 


PROXIMAL  SEG- 
MENT OF  CO- 
LON (affer 
ent  limb  of 
intesti  n  a  l 
loop) 


--—   DUODENUM 


PANCREAS 


DUODENO- 

COLIC 
ISTHMUS 


SMALL    IN- 
TESTINE 

(efferent 

LIMB    OF 

intestinal 
loop) 


ILEO-COLIC 
JUNCTION 


Fig.  110. — The  same  view,  from  another  specimen. 


DVODENO-COLIC ISTUMU8.  57 

maintained  throughout  its  extent.  Hence  the  mesentery  is  of 
equal  width  in  all  its  parts  within  the  loop,  only  drawn  out,  i.  e., 
away  from  the  vertebral  column,  in  accordance  with  the  length 
of  the  loop.  In  the  next  stage  (Fig.  Ill,  II.)  the  increase  in  the 
length  of  the  intestine  is  accompanied  by  a  corresponding  widen- 
ing of  the  mesentery.  The  points  1  and  2  are  still  approximately 
the  same  distance  apart  as  in  the  earlier  stage,  but  the  increase  in 
the  length  of  the  tube  between  these  points  forces  the  two  limbs  of 
the  loop  to  abandon  their  early  parallel  course,  and  to  form 
curved  lines  with  the  concavity  turned  toward  the  mesenteric 
attachment.  In  this  condition  the  mesentery  consequently  forms 
a  widely  expanded  membrane  framed  by  the  intestine  and  nar- 
rowing between  the  points  1  and  2  to  a  neck  or  isthmus  which 
effects  the  transition  between  the  expanded  segment  surrounded 
by  the  intestine  and  the  rest  of  the  dorsal  primitive  mesentery. 
Finally  in  the  stage  represented  in  Fig.  Ill,  III.,  the  increase 
in  the  length  of  the  small  intestine  has  reached  a  point  where  a 
single  curve  is  no  longer  sufficient  for  the  accommodation  of  the 
growth.  Consequently  the  tube  now  appears  coiled  and  convo- 
luted, and  the  mesentery,  as  it  is  attached  to  the  gut,  of  necessity 
follows  all  the  twists  and  appears  fluted  or  pleated  in  its  distal  at- 
tached portion. 

If  we  now  carefully  examine  the  conditions  presented  by  the 
intestine  and  mesentery  in  a  form  like  Tamandua  (Figs.  107  and 
108)  we  will  find  that  they  correspond  to  the  developmental  facts 
thus  far  considered.  The  termination  of  the  duodenum  (1)  and 
the  bend  in  the  colon  (2)  mark  the  two  points  at  which  in  the 
primitive  schema  (Fig.  Ill,  I.)  the  umbilical  loop  begins  and  ter- 
minates. The  proximal  of  these  two  points  (1)  corresponds  to  the 
termination  of  the  duodenum,  which  segment  extends  from  here 
cephalad  to  the  pyloric  extremity  of  the  stomach.  The  distal 
point  (2)  is  placed  on  the  colon  where  the  returning  limb  of  the 
loop  resumes  the  original  median  vertical  course  of  the  large  in- 
testine. These  two  points  mark  the  neck  of  the  loop,  which  we 
can  describe  as  the  duodeno-colic  neck  or  isthmus. 


58  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

The  same  condition  is  well  shown  in  the  intestinal  canal  of  the 
snapping  turtle  (Fig.  1 1 3).  The  duodenum  and  colon  approach 
each  other  very  closely  at  the  isthmus  and  between  these  points 
the  convolutions  of  the  intestine  extend  in  a  wide  circle.  We 
will  find  this  approximation  of  duodenum  and  colon  a  feature 
which  persists  throughout  all  the  later  developmental  stages  of 
the  higher  vertebrates  and  has  an  important  bearing  on  the  final 
arrangement  of  the  intestinal  canal  in  the  human  adult. 

Further  Changes  in  the  Development  of  the  Human  Alimentary 
Canal.  Rotation  of  the  Intestine.  Formation  of  the  Segments  of  the 
Colon.  Final  Permanent  Relations  of  the  Segments  of  the  Intestinal 
Tube. — The  next  important  stage  leading  up  to  the  final  adult  dis- 
position of  the  intestine  in  man  and  the  higher  mammals  is  the 
rotation  of  the  portions  developed  from  the  two  limbs  of  the  primi- 
tive loop  around  an  oblique  axis  drawn  from  the  duodeno-colic 
isthmus  to  the  apex  of  the  loop.  The  portion  of  the  large  in- 
testine, developed  from  the  ascending  limb  of  the  loop,  moves 
in  the  third  month  to  the  middle  line,  coming  into  contact  with 
the  ventral  abdominal  wall.  From  here  the  large  intestine  passes, 
ventrad  of  the  jejuno-ileal  coils,  toward  the  cephalic  end  of  the 
abdominal  cavity  and  lies  transversely  along  the  greater  curva- 
ture of  the  stomach.  The  growing  coils  of  the  small  intestine 
crowd  the  colon  more  and  more  cephalad.  In  the  fourth  month 
the  caecum  turns  to  the  right,  coming  into  contact  with  the 
caudal  surface  of  the  liver,  ventrad  of  the  duodenum,  and  subse- 
quently reaches  the  ventral  surface  of  the  right  kidney.  As  the 
result  of  this  rotation  the  ileo-colic  junction,  caecum  and  succeed- 
ing portion  of  the  colon  are  carried  from  the  original  position  in 
the  distal  and  left  part  of  the  abdomen  cephalad  and  to  the  right 
across  the  proximal  (duodenal)  portion  of  the  small  intestine, 
while  the  coils  of  the  jejuno-ileum,  developed  from  the  descend- 
ing limb  and  apex  of  the  loop,  are  turned  in  the  opposite  direction, 
caudad  and  to  the  left  underneath  the  preceding  (Figs.  114  and 
115).  This  change  in  the  relative  position  of  the  parts  of  the 
intestinal  tract  and  the  resulting  altered  bearing  of  the  colon  to 


DISPOSITION  OF  TEE  PRIMITIVE  MESENTERY.  59 

the  duodenum  will  be  best  appreciated  by  considering  in  the  first 
place  the  effect  of  the  change  on  the  arrangement  of  the  prim- 
itive mesentery  and  the  intestinal  vessels,  and  secondly  by  re- 
peating actually  the  rotation  in  the  intestinal  tract  of  a  mammal 
(cat)  in  which  the  adult  arrangement  of  the  intestine  and  peri- 
toneum permits  us  to  perform  the  manipulations  and  note  the 
result. 

I.  Effect  of  Rotation  on  the  Disposition  of  the  Primitive  Mesentery 
and  on  the  Relative  Position  of  Duodenum  and  Colon,  and  Consequent 
Arrangement  of  the  Intestinal  Blood  Vessels. — It  will  be  appreciated 
that  in  Fig.  Ill,  representing  a  profile  view  of  the  original  ar- 
rangement, or  in  Figs.  107  and  108,  showing  the  intestinal  canal 
of  Tamandua,  the  left  layer  of  the  primitive  mesentery  is  turned 
toward  the  observer.  The  membrane  is  seen  to  pass  from  the  ven- 
tral aspect  of  the  vertebral  column  and  aorta,  through  the  narrow 
neck  of  the  duodeno-colic  isthmus,  to  expand  in  the  manner  al- 
ready indicated  toward  its  intestinal  attachment.  In  the  rotation 
of  the  intestine  the  twist  takes  place  at  the  duodeno-colic  neck, 
carrying,  as  already  stated,  the  large  intestine  cephalad  and  to  the 
right,  while  the  jejuno-ileum  is  turned  in  the  opposite  direction 
caudad  and  to  the  left.  During  this  rotation  the  duodeno-jejunal 
angle  (Figs.  114,  J?  and  115,  ^)  passes  to  the  left  underneath  the 
proximal  segment  of  the  colon,  which  now  lies  ventrad  and  to 
the  right  of  the  duodenal  portion  of  the  small  intestine.  The 
mesenteric  peritoneum,  occupying  the  bight  of  the  umbilical  loop, 
will,  after  the  rotation,  in  the  left  profile  view  shown  in  Fig. 
104,  A  and  B,  turn  its  original  right  leaf  toward  the  beholder, 
i.  e.,  toward  the  left,  while  the  original  left  leaf  is  turned  toward 
the  right. 

Observation  of  the  difference  in  the  position  of  the  ileo-colic 
junction  will  still  further  accentuate  the  change  in  the  relative 
position  of  the  parts  which  has  been  effected  by  the  rotation.  In 
the  primitive  condition  shown  in  Fig.  104,  A,  the  ileum  enters 
the  large  intestine  from  right  to  left,  and  the  concavity  of  the 
csecal  bud  turns  its  crescentic  margin  ventrad  and  to  the  right. 


60  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

After  rotation  is  accomplished  (Fig.  104,  B  and  C,  and  Fig. 
115)  the  ileo-colic  entrance  takes  place  in  the  opposite  direction, 
from  left  to  right  and  the  caecum  turns  its  concave  margin  caudad 
and  to  the  left. 

Figs.  116  and  117  show  the  intestinal  tract  of  Tamandua  bivittata 
arranged  so  as  to  correspond  to  the  human  embryonic  condition 
after  rotation.  The  caecum  has  been  brought  up  and  to  the  right 
across  the  proximal  duodenal  portion  of  the  small  intestine,  while 
the  jejuno-ileal  coils  have  been  turned  down  and  to  the  left.  The 
rotation  has  been  accomplished  by  a  twist  at  the  duodeno-colic 
isthmus,  and  the  original  right  leaf  of  the  mesentery  has  become 
the  left  and  vice  versa.  Comparison  with  Figs.  107  and  108,  rep- 
resenting the  condition  before  rotation  in  the  same  animal,  will 
indicate  the  changes  which  have  been  accomplished  by  imitating 
the  course  of  development  followed  in  the  higher  mammals. 

Failure  of  rotation  and  arrest  of  development  at  the  primitive 
stage,  with  consequent  persistent  embryonic  condition  of  the 
mesentery,  occurs  occasionally  in  man.  Such  cases  have  been 
reported  by  W.  J.  Walsham,  in  St.  Barthol.  Hosp.  Rep.,  London, 
Vol.  16.  The  following  four  instances  of  this  condition,  taken 
from  the  Columbia  University  museum,  will  illustrate  the  disposi- 
tion of  the  abdominal  contents. 

Fig.  118  shows  the  arrangement  of  the  abdominal  viscera  in 
an  adult  female  body.  Beginning  at  the  pyloric  extremity  of  the 
stomach  the  entire  course  of  the  duodenum  can  be  overlooked  and 
its  continuation  into  the  jejuno-ileal  division  traced.  The  small 
intestines  ocicupy  the  ventral  and  right  part  of  the  cavity.  The 
ileo-colic  junction  is  placed  in  the  lower  left-hand  corner  of  the 
abdomen .  and  the  small  intestine  enters  the  large  from  right  to 
left,  the  ascending  colon  is  situated  to  the  left  of  the  median  line 
and  at  its  point  of  transition  into  the  segment  representing  the 
transverse  colon  is  connected  by  several  adhesions  with  the  ventral 
surface  of  the  duodenum.  The  transverse  colon,  folded  into 
several  coils  bound  together  by  adhesion,  occupies  the  upper  left 
portion  of  the  abdomen. 


PLATE   XLIX. 


1.  11.  111. 

Fig.  111. — Schematic  representation  of  the  development  of  the  mesentery  of  the  umbilical  loop. 


STOMACH 


ILEO-COLIC 
JUNCTION 
AND    VALVE 


Fig.  112. — Alimentary   canal,    isolated   and   in   section,   of   Echelus    conger,    the 
conger  eel.     (Columbia  University  Museum,  No.  1812.) 


PLATE    L. 


BEGINNING    OF 
MID-GUT 
DUODCNO-COLIC 
ISTHMUS 


PANCREAS 


ILEO-COLIC 
JUNCTION 


MID-GUT  FORM- 
ING APEX  OF 
I  N  T  E  S  T  I  N  AL 
LOOP 


Fig.  113. — Chelydra  serpenfina,  snapping  turtle;  intestinal 
canal,  pancreas,  and  spleen,  isolated.  (Columbia  University 
Museum,  No.  1369.) 


2.3 


to  H 


ag 


lO    4) 
.-a 

o  a 


< 


Sw 
U 


PLATE    LII. 


PYLORO- 
DUODENAL 
JUNCTION 
PANCREAS 


R.    LOBE   OF 
LIVER 


R.  KIDNEY3 


ILEO-COLIC 
JUNCTION 


LEFT    LOBE 
OF     LIVER 


STOMACH 

GREAT 
OMENTUM 
MESODUO- 
DENUM  WITH 
CONTAI  NED 
PANCREAS 


DUODENO- 
JEJUNAL 
ANGLE 


SMALL 
INTESTINE 


Fig.  116. — Abdominal  viscera  of  Tamandua  hirittata,  with  the  intestine  rotated  to  correspond 
to  the  development  in  the  human  subject.     (From  a  fresh  dissection.) 


PLATE    LIII. 


DESCENDING 
DUODENUM 


SLEO-COLIC 
JUNCTION 


STOMACH 


PANCREAS 


TERMINAL 
BEND     OF 

COLON 
DUODENO- 
JEJUNAL 
ANGLE 


Fig.  117. — The  same  yiew  as  Fig.  116,  from  another  specimen. 


PLATE    LIV. 


DUODENUM 


SMALL 
INTESTINE 


STOMACH 


SPLENIC 
FLEXURE 
SEGMENT    COR- 
RESPONDING 
TO  TRANSVERSA 
COLON 
ASCENDING   COLO\" 


ILEO-COLIC 
JUNCTION 


APPENDIX 


Fig.  118. — Abdominal  viscera  of  adult  human  female,  in  a  case  of  arrested  rota- 
tion of  the  intestines.     (Columbia  University  Museum,  Study  Collection.) 


DUODENUM 


PRIMITIVE 
PARIETAL 
PERI  TO- 
NEUM  OF 
RIGHT 
LUMBAR 
REGION 


PRIMITIVE  MES- 
ENTERY COM- 
MON TO  SMALL 
I  N  T  E  ST  I  N  E 
AND  NON-RO- 
TATED   COLON 


ILEOCOLIC 
JUNCTION 
DORSAL 
SURFACE 


Fig.  119. — The  same  preparation  with  the  intestinal  coils  displaced  upward  and  to  the  left. 


PLATE    LV. 


DUODENUM 


ASCCNDIN 
COLON 


STOMACH 


IRREGULAR 

TRANSVERSE 

COLON 


ILEOCOLIC 
JUNCTION 

DESCENDING 
COLON 


OMEGA    LOOP 


Fig.  120.— Abdominal  viscera  of  adult  human   male ;  non-rotation   of  intestine. 
(Columbia  University  Museum,  Study  Collection.) 


DUODENUM 


SMALL 
INTESTINE 


STOMACH 

BEND  OF  COLON  COR- 
RESPONDING TO  HE- 
PATIC   FLEXURE 

SPLENIC    FLEXURE 


DUODENOCOLIC 
ISTHMUS 

ASCENDING    COLON 

IRREGULAR    TRANS- 
VERSE   COLON 


DESCENDING    COLON 
ILEOCOLIC  JUNCTION 


Fig.  121. — Abdominal  viscera  of  adult  human  male;    non-rotation  of  intestine.      (Columbia 
University  Museum,  Study  Collection.) 


•%. 


»o 


NON-ROTATION  OF  INTESTINE  IN  ADULT.  61 

Fig.  119,  taken  from  the  same  specimen,  shows  the  entire  mass 
of  intestines  lifted  up  and  turned  to  the  left,  exposing  the  back- 
ground of  the  abdominal  cavity  lined  by  parietal  peritoneum. 
The  duodenum  is  still  entirely  free  and  non-adherent  to  the 
parietal  peritoneum.  The  continuity  of  the  meso-duodehum  with 
the  jejuno-ileal  mesentery  is  well  shown.  The  primitive  right 
leaf  of  the  mesentery  is  turned  to  the  observer.  This  laj^er  after 
completed  rotation  would  form  the  left  layer  of  the  adult  mes- 
entery of  the  jejuno-ileum. 

Fig.  120  illustrates  another  instance  of  the  same  condition  in 
the  adult.  In  this  case  the  duodenum  was  coiled  twice  upon  itself 
and  adherent  to  the  prerenal  parietal  peritoneum. 

Fig.  121,  presenting  the  same  adhesion  of  the  duodenum,  illus- 
trates very  perfectly  the  persistence  of  the  narrow  duodeno-colic 
isthmus  in  cases  of  non-rotation,  as  well  as  the  development  of 
the  different  segments  of  the  adult  tract  from  the  limbs  of  the 
embryonal  umbilical  intestinal  loop. 

It  will  be  observed  that  beyond  the  duodeno-colic  isthmus  the 
coils  of  the  jejuno-ileum  have  resulted  from  the  increase  in  length 
of  the  descending  limb,  the  apex  and  the  proximal  part  of  the 
ascending  or  recurrent  limb,  carrying  the  ileo-colic  junction  and 
caecum.  The  remainder  of  the  ascending  limb,  terminating  in 
the  embryonic  condition  at  the  splenic  flexure  by  passing  into 
the  descending  colon,  has  in  the  course  of  further  development 
in  this  individual  produced  a  straight  segment — the  misplaced 
ascending  colon — and  a  convoluted  and  bent  representative  of 
the  normal  transverse  colon. 

The  same  disposition  of  the  large  intestine  may  be  noted  in  the 
other  preparations. 

Fig.  122  shows  an  instance  of  non-rotation  observed  in  the  hu- 
man infant  at  two  years  of  age. 

Fig.  123,  taken  from  a  foetus  at  term,  shows  the  result  of  failure 
to  completely  rotate  in  the  region  of  the  caecum  and  ileo-colic 
junction.  The  rest  of  the  large  intestine  has  rotated  as  usual  and 
assumed  the  normal  position.     The   terminal   ileum,  however, 


62  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

passes  behind  the  caecum  and  enters  the  large  intestine  on  its 
right  side ;  the  caecum  is  turned  upwards  and  to  the  right  and 
the  appendix  lies  ventrad  of  the  beginning  of  the  ascending 
colon.  In  order  to  produce  the  normal  arrangement,  shown  in 
Fig.  124,  taken  from  another  foetus  at  term,  it  would  be  necessary 
to  turn  the  csecum  and  ileo-colic  junction  in  Fig.  123  through 
half  a  circle.  The  caecum  would  then  turn  upwards  and  to  the 
left,  the  ileum  entering  the  large  intestine  from  left  to  right,  and 
the  appendix  would  be  placed  behind  the  caecum  and  ileo-colic 
junction.  Figs.  125  and  126  show  the  normal  and  abnormal 
arrangement  presented  by  these  two  preparations  diagrammatic- 
ally.  The  instances  in  which  in  the  adult  the  ileo-colic  entrance 
is  placed  on  the  right  side  of  the  large  intestine  and  in  which 
the  appendix  is  situated  laterad  of  the  ascending  colon  unques- 
tionably find  their  explanation  in  the  failure  of  the  intestine  to 
completely  rotate  at  the  ileo-colic  junction. 

The  resulting  conditions  are  shown  in  Figs.  127  and  128,  taken 
from  adult  human  subjects  in  which  the  final  stage  of  rotation  of 
the  large  intestine  has  not  taken  place. 

In  Fig.  127  the  terminal  ileum  is  sharply  bent  on  itself  and 
adherent  to  the  prerenal  parietal  peritoneum.  It  passes  from 
right  to  left  and  downwards  to  enter  the  right  posterior  circum- 
ference of  the  large  intestine.  The  caecum  is  turned  cephalad  and 
the  appendix  is  in  contact  with  the  right  lobe  of  the  liver.  The 
caecum  passes  with  a  sharp  bend  into  the  obliquely  directed  as- 
cending colon. 

In  Fig.  128  the  ileum  enters  the  colon  from  the  right  and 
below.  The  apex  of  the  caecum  is  turned  cephalad  and  to 
the  right  and  the  appendix  extends  beneath  peritoneal  adhe- 
sions along  the  lateral  border  of  the  proximal  segment  of  the 
colon. 

In  the  next  place  it  is  desirable  to  clearly  understand  the  vas- 
cular supply  of  the  intestine  before  and  after  rotation  and  the 
final  relation  of  the  superior  mesenteric  artery  to  the  transverse 
portion  of  the  duodenum. 


DEVELOPMENT  OF  THE  AORTAL  SYSTEM.  63 

Development  of  Aortal  Arterial  System. 

The  thoracic  and  abdominal  aortse  are  at  first  double,  the  first 
aortic  arches  continuing  as  so-called  "primitive  aortse"  ventrad 
of  the  vertebral  column  to  the  caudal  end  of  the  body. 

The  cephalic  portions  of  the  two  vessels  unite  in  the  chick  on 
the  third  day  and  from  this  point  fusion  into  a  single  vessel  pro- 
ceeds slowly  caudad. 

In  the  rabbit  the  fusion  of  the  primitive  aortse  begins  on  the 
ninth  day  in  the  region  of  the  lung-buds  and  progresses  from  here 
caudad  until  by  the  sixteenth  day  a  single  aorta  is  formed  (Fig. 
129). 

That  the  entire  descending  aorta  in  nian  results  from  the  fusion 
of  two  vessels  is  shown  by  the  rare  cases  in  which  the  aorta  is 
divided  throughout  its  entire  length  by  a  septum. 

The  arteries  of  the  allantois  are  originally  the  terminations  of 
the  primitive  aortse.  After  fusion  of  the  primitive  aortse  to  form 
the  abdominal  aorta  the  allantoic  arteries,  now  passing  as  the  um- 
bilical arteries  to  the  placenta,  appear  as  the  branches  of  bifurca- 
tion of  the  abdominal  aorta,  in  the  same  way  as  the  common  iliacs 
do  in  the  adult. 

They  furnish  branches,  which  at  first  are  very  small,  to  the 
budding  posterior  extremities  and  the  pelvic  viscera.  In  time 
these  rudiments  of  the  future  external  and  internal  iliac  arteries 
become  larger,  but  as  the  umbilical  arteries  continue  to  develop 
throughout  the  entire  intra-uterine  period  they  appear  even  in 
the  foetus  at  term  as  end  branches  of  the  aorta,  a  condition  which 
is  only  changed  after  birth  by  the  obliteration  of  the  umbilical 
arteries  and  their  conversion  into  the  lateral  ligaments  of  the 
bladder,  while  the  iliac  vessels  now  appear  as  the  terminal  aortic 
branches.  The  statement  that  the  umbilical  arteries  appear  as 
the  terminal  branches  of  the  embryonal  aorta  requires  to  be  modi- 
fied in  the  following  respect : 

When  the  allantois  develops  its  arteries  are  in  fact  end- 
branches  of  the  two  primitive  aortse.  After  their  fusion  and 
after  the  formation  of  the  single  aorta  this  vessel  is  continued  be- 


64  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

yond  the  umbilical  arteries  as  a  small  trunk,  the  caudal  artery  or 
rudiment  of  the  adult  sacralis  media.  Consequently  the  umbilical 
arteries  are  really  lateral  branches  of  a  median  vessel,  viz.,  aorta 
abdominalis  and  arteria  sacralis  media.  But  as  the  umbilical  ves- 
sels are  very  large  and  the  caudal  aorta  very  small,  the  former, 
even  under  these  conditions,  appear  as  the  real  terminal  branches 
of  the  abdominal  aorta. 

The  arteries  supplying  the  yolk-sac  and  subsequently  the  intes- 
tinal canal  are  the  vitelline  or  omphalo-mesenteric.  At  first  they 
are  branches  derived  from  the  two  primitive  aortae,  and  after  the 
fusion  of  these  vessels  they  arise  from  the  resulting  single  abdom- 
inal aorta.  The  omphalo-mesenteric  arteries  are  at  first  multiple 
and  later  are  reduced  to  two.  When  the  primitive  intestine  loses 
its  original  close  contact  with  the  vertebral  column  and  the  com- 
mon dorsal  mesentery  develops,  the  two  omphalo-mesenteric  ar- 
teries unite  to  form  a  single  vessel,  running  between  the  layers  of 
the  mesentery.  After  a  short  course  this  artery  divides  again  into 
two  branches,  passing  one  on  each  side,  around  the  intestinal  tube, 
which  has  in  the  meanwhile  become  closed.  Ventrad  of  the  in- 
testine these  branches  reunite  so  that  the  gut  is  surrounded  by  a 
vascular  circle.  The  left  half  of  this  loop  becomes  obliterated 
and  the  trunk  of  the  omphalo-mesenteric  artery  now  passes  on 
the  right  side  of  the  intestine  to  the  umbilicus.  The  peripheral 
segment  of  the  omphalo-mesenteric  artery  disappears  with  the 
cessation  of  the  vitelline  circulation.  The  proximal  portion,  sit- 
uated between  the  layers  of  the  mesentery,  gives  numerous  anas- 
tomosing branches  to  the  intestine  and  is  converted  into  the  main 
trunk  of  the  superior  mesenteric  artery. 

The  derivation  of  the  superior  mesenteric  as  the  fully  developed 
proximal  segment  of  the  embryonic  omphalo-mesenteric  artery 
passing  to  the  yolk-sac  is  responsible  for  the  rare  anomaly  in  the 
adult  of  a  branch  of  the  superior  mesenteric  artery  continuing 
beyond  the  intestine  to  the  umbilicus.  I  have  encountered  one 
instance  of  this  persistence  of  the  intra-abdominal  portion  of  the 
omphalo-mesenteric  artery  in  a  male  subject  54  years  of  age.     A 


PLATE    LVII. 


POSTCAVAL 
VEIN 


R.    KIDNEY 
PYLORUS 


DUODENUM 


TERMINAL. 
ILEUM 


APPENDIX- 


BLADDER 


STOMACH 


PANCREAS 


TRANSVERSE 

COLON 
GREAT 
OMENTUM 
DESCENDING 

COLON 
DUODENOJEJ- 
UNAL ANGLE 
CUT    MESENTERY 
OFSMALL   INTES- 
TINE 

OMEGA 
LOOP 


Fig.  124.— Human  foetus  at  term ;  abdominal  viscera,  hardened  in  situ  ;  normal 
position  of  completely  rotated  caecum  and  appendix.  (Columbia  University  Museum, 

No.  1814.) 


Fig.  125. — Just  before  final  rotation  of  caecum  Fig.  126. — Rotation  completed.    Con- 

and  terminal  ileum.  Concavity  of  cajcum  directed  cavity   of  ca?cum   turns  caudad  and  to 

cephalad  and  to  right.     Terminal  ileum  enters  left.     Terminal  ileum  enters  colon  from 

colon  from  right  to  left.  left  to  right. 

Figs.  125,  12(). — Schematic  representation  of  final  stages  in  rotation  of  caecum  and  large  intestine. 


PLATE    LVIII. 


TERMINAL 
ILEUM 


GREAT 

OMENTUM 


Fig.  127. — Adult  human  sulyect  with  non-rotated  ciPcum. 
from  right  to  left  to  enter  right  side  of  colon. 


The  terminal  ileum  turns  eaudad 


ASC.    COLON 


APPENDIX  AD 
HERENT  TO 
LATERAL  AS- 
PECT OF  ASC. 
COLON  AND 
TO  ILIAC  PA- 
RIETAL PERI- 
TONEUM 


GREAT 
OMENTUM 


TERM.NAL 
ILEUM 


Fig.  128. — Adult  humun  suhjcct  with  non-rotated  ca'cuin.  tlic  ilcuin  entering  large  intestine 
from  the  right  and  behind,  and  the  appendix  placed  to  the  right  of  the  ascending  colon.  '.From 
a  fresh  dissection.) 


PLATE    LIX. 


PRIMITIVE, 
AORTiE 


TRUNCUS 
ARTERIOSUS 


PRIMITIVE 
VENTRICLE 

VENOUS    END 
OF       HEART. 
TUBE 
VITELLINE     VEINS     RE- 
TURNING BLOOD  FROM 
VASCULAR    AREA 

VITELLINE  ARTERIES 
CARRYING  BLOOD  TO 
VASCULAR    AREA 

CONTINUATION  OF 
DOUBLE  AORTA  TO 
CAUDAL  POLE  OF  EM- 
BRYO 


Fig.  129. — Diagrams  illustrating  the  arrangement  of  the   primitive   heart 
and  aortic  arches.     (After  Heisler,  modified  from  Allen  Thompson.) 


GASTRIC    (coronary] 
ART. 


PYLORIC    ART. 

A-  GASTRO-EPIPLOICA 

DEXTRA 

HEPATIC    ARTERY 

A.   PANCREATICO-DUODEN- 

ALIS    SUP. 
A.   PANCREATICO-DUODEN- 
ALIS    INF. 
SUP.   MESENTERIC    ART. 
GIVING     OFF     VASA     INTES- 
TINI    TENUIS 


A.    COLICA    DEXTRA 


VITELLINE    DUCT 


ILEOCOLIC     ART. 
OECAL    BUD 


A.  GASTRO-EPIPLOICA  SIN- 
ISTRA 
SPLEEN 


SPLENIC    ART. 


ABDOMINAL   AORTA 
A.    COLICA    MEDIA 


NF.    MESENTERIC    ART. 


A.    SIGMOIDEA 


Fig.  130. — Diagrammatic  representation  of  the  arteries  proceeding  to  the  alimentary 
canal  and  appendages  prior  to  rotation  of  intestine  (stage  of  simple  umbilical  loop). 


PLATE    LX. 


GASTRIC    (coronary) 
ART. 


PYLORIC    ART. 
HEPATIC    ART. 

A.  PANCREATICO- 
DUODENALIS  SUP 
A.  PANCREATICO- 
DUODENALIS    INF 


ABDOMINAL   AORTA 


A.  GASTRO-EPIPLOICA 
SINISTRA 


SPLENIC    ART. 
A.  GASTRO-EPIPLOICA 
DEXTRA 


SUP.    MESENTERIC    ART. 


A.    COLICA    MEDIA 

A.    COLICA    DEXTRA 
INF.    MESENTERIC    ART. 
ILEOCOLIC   ART. 


Fig.  131. — Diagrammatic  representation  of  the  arteries  of  the  alimentary  canal 
in  the  first  stage  of  intestinal  rotation,  showing  relation  of  superior  mesenteric 
artery  to  the  transverse  portion  of  the  duodenum. 


PYLORIC    ART 
HEPATIC    ART. 


A      PANCREATICO-DUOD.    SUP. 


A.    PANCREATICO-DUOD.    INF 


A.    COLICA    MEDIA 


INF     MESENTERIC   ART 


GASTRIC    ART. 

A.  GASTRO-EPIPLOICA    SINISTRA 


-SPLEEN 


A.    GASTRO-EPIPLOICA    DEXTRA 
SPLENIC    ART. 


PANCREAS 

SUP.    MESENTERIC    ART. 


A.   COLICA    DEXTRA 


1/ 


Fig.  132. — Arteries  of  alimentary  canal  in  the  later  stages  of  intestinal  rotation. 


PLATE    LXI. 


AORTA 

GASTRIC    ART. 

HEPATIC       ART. 

WITH      PYLORIC 

BRANCH 

DUODENUM 

A.      PANCREATICO- 

DUODENALIS  SUP. 

A.  GASTRO-EPIPLO- 

ICA    DEXTRA 

PANCREAS 


A.  PANCREATICO- 
DUOOENALIS  INF. 
A.   COLICA    MEDIA 

A.  COLICA  DEXTRA 


A.    GASTRO-EPIPLO- 
ICA    SINISTRA 


SPLENIC  ART. 


SUP.     MESENTERIC 
ART. 


VASA    INTESTINI 

TENUIS 
A.  COLICA 
SirriSTRA 
INF.  MESENTERIC 

ART. 

A.  SIGMOIDEA    AND 
SUP.    H>EMOR- 
RHOIDAL  ART. 


Fig.   133.^ — Final  arrangement  of  arteries  of  alimentary  canal  after  completed 
rotation  of  the  intestines. 


GASTRIC  (coro- 
nary)  ART. 
HEPATIC   ART 

A.     PANCREATICO- 
DUOD.    SUP. 
A.   GASTRODUOD. 
DUODENUM 

A.   PANCREATICO- 
DUOD.   INF. 
iUP.     MESENTERIC 
ART. 


STOMACH 

A.  GASTRO-EPi- 

PLOICA   SINISTRA 


SPLENIC   ART. 

PANCREAS 

AORTA 

A     COLICA    MEDIA 
A.    COLICA     DEXTRA 

INF.    MESENTERIC 
ART. 


Fig.  134. — Schematic  representation  of  intestinal  arterial  supply  from  superior 
mesenteric  artery  iu  cases  of  arrested  rotation  of  the  intestine. 


PLATE    LXir. 


GREAT 

OMENTUM 

TURNED   UP 


LIVER 

(B)  terminal  bend 
of  colon    cor- 
responding   to 
splenic  flexure 
right  kidney 


ILEOCOLIC 
JUNCTION 


PANCREAS 
SPLEEN 

(A)    DUOOCNUM 


-      MESENTERY 


Fig.  135. — Abdomiual  viscera  of  cat;  great  omeutum  raised;  iutestiiies  turned  down  and  to 
left.     (From  a  fresh  dissection.) 


PLATE    LXIII. 


GASTROHEPATIC 

OMENTUM 

HEPATIC    ART. 

BILE-DUCT 

PORTAL   VEIN 

PYLORUS,   LINE  OF 

DIVIDED    GREAT 

OMENTUM 


DUODENUM 
PANCREAS 


SUP.  MESENTERIC 
ART.  ENTERING 
MESENTERY  AT 
DUODENOCOLIC 
ISTHMUS  (X.) 


SMALL   INTESTINE 


LIVER,   L.  LOBE 


PYLORIC   ART. 

SPIGELIAN    LOBE 
STOMACH, DORSAL SUR. 
LINE  OF  CUT  G.  OMENTUM 
GASTRIC   ART. 

SPLENIC    ART. 
SPLEEN 


COLON,  TERMI- 
NAL   PORTION 


COLON,    PROXI- 
MAL   PORTION 


ILEOCOLIC   JUNCTION 
OCCUM 


Fig.  136. — Abdominal  viscera  of  cat,  hardened  ;  omentum  removed  to  di.splay  derivation  of 
intestines  from  umbilical  loop  and  the  relation  of  the  superior  mesenteric  artery  and  common 
dorsal  mesentery  to  the  small  and  large  intestines.     (Columbia  University  Museum,  No  728.) 


PLATE    LXIV. 


DUODENUM 

DUODENOCOLIC    ISTHMUS 

WITH     PANCREAS    AND 

SUP.    MESENTERIC    ART 

RIGHT    KIDNEY 


GREAT 
OMENTUM 
TURNED 
UP 


'  STOMACH 


SPLEEN 

TERMINAL 
BEND    OF 
COLON 
L.    KIDNEY 


LEOCOLIC 
JUNCTION 


Fig.  137. — Abdominal  cavity  of  cat.     (From  a  fresh  dissection.) 


DEVELOPMENT  OF  THE  INTESTINAL  ARTERIES.  65 

connective  tissue  strand,  containing  a  small  artery  derived  from 
the  superior  mesenteric  vessels,  extended  between  the  right  layer 
of  the  mesentery,  some  distance  from  its  attached  border,  and 
the  ventral  abdominal  wall  at  the  umbilicus.  The  vessel  which 
was  pervious  throughout,  was  the  size  of  one  of  the  digital  arteries. 

Hjrrtl  has  observed  the  same  variation.  An  example  of  par- 
tial persistence  of  the  omphalo-mesenteric  artery  in  the  adult  is 
well  seen  in  the  case  of  Meckel's  diverticulum  shown  in  Fig.  37, 
where  the  arterial  vessel  continued  upon  the  diverticulum  repre- 
sents the  embryonic  omphalo-mesenteric  artery. 

The  remaining  intestinal  arteries  are  at  first  more  numerous  and 
paired.  In  man  and  most  mammals  they  are  early  reduced  in 
number,  passing  from  the  abdominal  aorta  to  the  dorsal  or  attached 
border  of  the  intestine,  between  the  two  peritoneal  layers  of  the 
primitive  dorsal  mesentery  (Fig.  104).  The  arterial  blood  supply 
of  the  intestinal  canal  then  presents  three  general  divisions : 

1.  Vessels  pass  from  the  proximal  part  of  the  abdominal  aorta  to 
the  stomach  and  pyloric  portion  of  the  duodenum.  This  set  of 
vessels  forms  the  rudiment  of  the  future  coeliac  axis.  With  the 
development  of  the  liver  and  pancreas  by  budding  from  the  duo- 
denum, and  with  the  appearance  of  the  spleen  in  the  mesoderm 
of  the  dorsal  mesentery,  branches  corresponding  to  these  organs 
(hepatic  and  splenic  arteries)  are  added  to  the  gastric  and  duo- 
denal vessels  and  the  adult  arrangement  of  the  coeliac  axis  is  thus 
obtained  (Figs.  130,  131,  132  and  133). 

These  vessels  have  an  important  bearing  on  the  formation  of 
the  adult  peritoneal  cavity  in  the  retro-gastric  space,  and  will  be 
considered  in  detail  below  with  that  portion  of  the  subject. 

2.  The  next  vessel  in  order  derived  from  the  aorta  and  supply- 
ing the  duodenum,  pancreas,  the  small  and  a  part  of  the  large  in- 
testine is  the  above-mentioned  superior  mesenteric  artery,  which 
arises  from  the  aorta  a  short  distance  caudad  of  the  coeliac  axis 
(Figs.  130,  131,  132  and  133). 

At  the  time  when  the  intestine  still  presents  the  primitive  ar- 
rangement of  the  umbilical  loop  (Figs.  104  and  130)  this  vessel 

5 


66  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

passes  between  the  layers  of  the  dorsal  mesentery  through  the 
narrow  duodeno-colic  neck  to  reach  the  two  limbs  and  the  apex 
of  the  intestinal  loop.  In  its  course  it  gives  off  successively 
branches  to  the  gut  from  each  side.  Those  from  the  right  side 
of  the  main  vessel  pass  to  the  duodenum,  pancreas,  jejunum  and 
ileum.  Those  from  the  left  side  of  the  main  vessel  accede  in 
succession  to  the  colic  angle  of  the  isthmus,  the  proximal  por- 
tion of  the  colon,  the  caecum  and  the  ileo-colic  junction.  The 
terminal  portion  of  the  superior  mesenteric  artery  supplies  the 
ileum  near  the  ileo-colic  entrance.  After  rotation  it  will  be 
found  that  the  turn  has  occurred  at  the  point  X  (Fig.  130), 
i.  e.,  in  that  part  of  the  vessel  which  occupies  the  duodeno- 
colic  isthmus.  Hence  it  will  be  found  that  the  first  branches 
derived  from  the  right  side  of  the  primitive  superior  mesenteric 
artery,  supplying  the  duodenum  and  pancreas  (Art.  pancreatico- 
duodenalis  inferior)  still  arise  after  rotation  from  the  right  side. 
They  are  succeeded,  beyond  the  point  X,  by  the  original  highest 
left  branches  passing  to  colon,  caecum  and  ileo-colic  junction,  while 
all  the  original  right-sided  vessels,  except  the  inferior  pancreatico- 
duodenal, appear  now  as  branches  from  the  left  side  of  the  main 
artery,  supplying  the  coils  of  the  jejuno-ileum.  Hence  in  the 
adult  (Fig.  138)  the  succession  of  branches  derived  from  the 
right  or  concave  side  of  the  superior  mesenteric  artery  is  as 
follows : 

1.  Arteria  pancreatico-duodenalis  inferior. 

2.  Arteria  colica  media. 

3.  Arteria  colica  dextra. 

4.  Arteria  ileo-colica. 

On  the  other  hand,  the  first  branches  from  what  has  now  be- 
come the  left  or  convex  side  of  the  vessel  are  the  original  lower 
right-hand  vessels  to  the  small  intestine  developed  from  the  de- 
scending limb  of  the  loop.  Hence  in  the  adult  the  left  side 
of  the  superior  mesenteric  vessel  gives  rise  to  the  vasa  intestini 
tenuis. 

3.  The  caudal  intestinal  arterial  branch  derived  from  the  aorta 


INTESTINAL  ROTATION  IN  THE  CAT.  67 

is  the  inferior  mesenteric  artery  supplying  parts  of  the  transverse 
colon,  the  descending  colon,  sigmoid  flexure  and  rectum  (Figs. 
130,  131,  132,  and  133). 

On  the  other  hand  in  the  cases  of  non-rotation  of  the  intestine 
as  above  described  in  Figs.  118-122,  the  embryonic  type  of  the  in- 
testinal arterial  supply  persists,  as  indicated  schematically  in  Fig. 
134.  Not  only  the  pancreatico-duodenalis  inferior,  but  all  the  re- 
maining branches  to  the  small  intestine  are  derived  from  the  right 
side  of  the  superior  mesenteric  artery.  The  terminal  branches 
of  the  main  artery  supply  the  ileo-colic  junction,  while  the 
arterial  supply  of  the  large  intestine,  A.  colica  dextra  and  media, 
are  given  off  from  the  left  side  of  the  parent  vessel. 

II.  Demonstration  of  Intestinal  Rotation  in  the  Cat. — The  changes 
in  the  relative  position  of  the  different  intestinal  segments  and 
the  final  disposition  of  the  mesenteries  and  blood  vessels  can  best 
be  understood  by  the  direct  examination  of  the  abdominal  con- 
tents in  an  animal  whose  permanent  adult  arrangement  corre- 
sponds to  one  of  the  early  embryonal  human  stages,  and  in 
which  the  necessary  manipulations  can  readily  be  carried  out  and 
their  results  noted. 

It  is  doubtful  if  the  above  detailed  developmental  stages  in  man 
can  ever  be  clearly  comprehended  unless  the  student  will  for 
himself  examine  the  conditions  and  perform  the  manipulations 
in  one  of  the  lower  mammals. 

The  necessity  of  keeping  the  three  dimensions  of  space  in  mind 
and  the  fact  that  certain  structures  during  and  after  rotation  cover 
and  obscure  each  other,  make  diagrams  and  drawings  unsatis- 
factory unless  the  actual  examination  of  the  object  itself  is  com- 
bined with  their  study.  Fortunately,  among  the  common  do- 
mestic animals  of  convenient  size  easily  obtained  the  cat  answers 
every  purpose  of  this  study  admirably.  The  student  is  earnestly 
urged  to  pursue  his  study  of  the  development  and  adult  arrange- 
ment of  the  human  abdominal  viscera  and  peritoneum  in  the 
light  which  the  anatomy  of  this  animal  can  shed  on  the  compli- 
cated and  obscure  conditions  encountered  in  the  human  subject. 


68  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

The  plan  of  having  the  opened  abdominal  cavity  of  the  cat  di- 
rectly side  by  side  with  the  human  subject,  while  the  arrangement 
of  the  abdominal  viscera  and  peritoneum  is  considered,  cannot  be 
recommended  too  highly. 

Directions. — After  killing  the  animal  with  chloroform  the  ab- 
dominal cavity  is  to  be  freely  opened  by  a  cruciform  incision  and 
the  skin  flaps  turned  well  back  and  secured  in  this  position.  It 
is  well  to  select  a  male  animal  or  an  unimpregnated  female,  as  the 
size  of  the  pregnant  uterus  in  the  later  stages  renders  the  examina- 
tion of  the  abdominal  viscera  and  peritoneum  more  difficult. 

For  purposes  of  careful  study  and  comparison  of  the  vascular 
relations  of  the  abdomen,  it  is  highly  desirable  to  inject  the  ani- 
mal with  differently  colored  gelatine,  starch  or  plaster  of  Paris 
mass.  The  arterial  injection  can  be  made  through  the  carotid 
artery,  the  systemic  venous  injection  through  the  femoral  vein, 
and  the  portal  circulation  can  be  filled  after  opening  the  abdo- 
men, by  injection  through  the  superior  mesenteric  or  splenic 
veins.  Animals  prepared  in  this  manner  are  especially  useful 
for  the  study  of  the  upper  portion  of  the  abdominal  cavity 
and  of  the  peritoneal  relations  of  liver,  stomach,  spleen,  pan- 
creas and  duodenum.  They  may  be  kept  for  permanent  ref- 
erence in  a  5  per  cent,  solution  of  formaline  or  50  per  cent, 
alcohol. 

After  opening  the  abdominal  cavity  turn  the  great  omentum  up 
over  the  ventral  surface  of  the  thorax  and  secure  it  in  this  posi- 
tion, thus  exposing  the  underlying  intestines  completely  (Fig. 
135).  Trace  in  the  first  place  the  entire  course  of  the  intestinal 
tube  from  the  pyloric  extremity  of  the  stomach  down.  It  will  be 
noticed  that  the  first  portion  of  the  small  intestine  (duodenum) 
is  freely  movable,  completely  invested  by  peritoneum  and  attached 
to  the  dorsal  midline  by  a  mesoduodenum  between  the  layers  of 
which  a  portion  of  the  pancreas  is  seen. 

Following  the  duodenum  caudad  it  will  be  observed  that  the 
gut  can  be  traced  directly  continuous  with  the  remaining  coils  of 
the  small  intestine.     The  ileo-colic  junction  and  the  beginning  of 


INTESTINAL  CANAL   OF  CAT.  69 

the  large  intestine  are  marked  by  a  short  pointed  caecum.  The 
large  intestine  is  short,  as  it  is  in  all  carnivore  mammals,  and 
passes  from  the  caecum  almost  directly  down  into  the  pelvis. 

Take  the  caecum  and  the  first  portion  of  the  large  intestine  and 
turn  them  caudad  and  over  to  the  left  side  as  far  as  the  peritoneal 
connections  will  permit. 

Spread  out  the  coils  of  the  small  intestine  in  the  opposite  direc- 
tion, i.  e.,  over  to  the  right  side. 

The  arrangement  of  the  intestinal  tract  after  these  manipula- 
tions should  appear  as  shown  in  Figs.  136  and  137. 

It  will  be  seen  that  all  the  essential  features  described  for  the 
corresponding  stage  in  the  human  embryo  (Fig.  104,  A)  exist 
here.  The  proximal  portion  of  the  small  intestine  (duodenum) 
retains  its  freedom  and  mobility,  being  attached  to  the  ven- 
tral surface  of  the  vertebral  column  by  the  portion  of  the  prim- 
itive mesentery  which  now  constitutes  the  mesoduodenum. 
The  gut  itself  forms  a  bend  with  the  convexity  turned  to  the 
right. 

Observe  in  the  next  place  that  the  point  (Fig.  136,  X),  where 
small  intestine  and  colon  approach  each  other  closely,  marks  the 
situation  of  the  foetal  duodeno-colic  isthmus.  The  small  intestine 
at  this  point  corresponds  to  the  future  duodeno-jejunal  angle  as 
will  be  seen  after  rotation  has  been  accomplished. 

Recalling  the  development  of  the  jejuno-ileum  it  mil  not  be 
diflBcult  to  recognize  in  the  numerous  coils  of  small  intestine 
which  succeed  to  the  duodeno-colic  isthmus  the  results  of  the  in- 
crease in  length  of  the  descending  or  efferent  limb  of  the  human 
embryonal  umbilical  loop.  Tracing  these  coils  it  will  be  found 
that  the  terminal  portions  of  the  ileum  correspond  to  the  apex  and 
to  the  proximal  part  of  the  ascending  or  recurrent .  limb  of  the 
primitive  loop,  while  the  remainder  of  this  limb  furnishes  the 
caecum  and  the  next  succeeding  segment  of  the  large  intestine. 
Following  the  tube  up  to  this  point  the  colic  boundary  of  the  duo- 
deno-colic isthmus  will  be  reached;  from  here  the  short  large  in- 
testine of  the  carnivore  descends  straight  into  the  pelvis,  attached 


70  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

to  the  ventral  surface  of  the  vertebral  column  by  a  meso-colon 
which  corresponds  to  the  distal  part  of  the  original  primitive 
dorsal  mesentery. 

Now  with  the  parts  still  in  this  position  examine  carefully  the 
arrangement  of  the  mesentery  and  of  the  intestinal  blood  vessels. 
Starting  with  the  duodenum  it  will  be  seen  that  the  primitive 
sagittal  mesentery  of  this  portion  of  the  intestine  has  followed  the 
gut  in  its  turn  to  the  right,  so  that  the  original  right  layer  of  the 
sagittal  membrane  is  now  directed  dorsad  and  lies  in  contact  with 
the  parietal  peritoneum  which  invests  the  background  of  the  ab- 
dominal cavity  in  the  right  lumbar  region  below  the  liver  and 
covers  the  ventral  surface  of  the  right  kidney.  Beneath  this 
parietal  peritoneum  the  inferior  vena  cava  is  seen,  receiving  the 
right  renal  vein  and  ascending  to  enter  the  dorso-caudal  aspect 
of  the  right  lobe  of  the  liver.  If  now  we  assume  that  in  the 
cat  the  opposed  serous  surfaces  of  the  original  right  leaf  of  the 
mesoduodenum,  now  directed  dorsad,  and  of  the  parietal  peri- 
toneum adhere  to  each  other,  and  that  the  visceral  peritoneum 
covering  the  dorsal  surface  of  the  descending  duodenum  likewise 
becomes  obliterated  by  adhesion  to  the  subjacent  parietal  peri- 
toneum, we  will  obtain  the  arrangement  found  in  the  adult 
human  subject,  in  which  the  descending  duodenum  is  fixed  by 
adhesion  below  the  right  lobe  of  the  liver  and  ventrad  of  the 
medial  portion  of  right  kidney,  right  renal  vein  and  inferior  vena 
cava.  During  this  process  of  anchoring  the  head  of  the  pancreas, 
which  is  found  between  the  two  layers  of  the  free  mesoduodenum 
of  the  cat,  would  also  become  fixed  to  the  abdominal  background 
by  adhesion  of  the  original  right  leaf  of  the  mesoduodenum,  in- 
vesting what  has  now  become  the  dorsal  surface  of  the  pancreas,  to 
the  parietal  peritoneum.  The  original  left  layer  of  the  primitive 
mesoduodenum  would  then  appear  as  secondary  parietal  peri- 
toneum covering  what  has  now  become  the  ventral  surface  of  the 
transversely  disposed  head  of  the  gland.  The  stages  may  be 
represented  schematically  in  Figs.  138-140. 

Figs.  138  and  139  shows  the  arrangement  in  the  cat  where  a 


FIXATION  OF  DUODENUM  AND  PANCREAS.  71 

free  duodenum  and  mesoduodenum  exists,  with  the  pancreas 
included  between  its  layers.^ 

It  will  be  noticed  that  the  duodenum  in  the  cat  can  be  carried 
over  to  the  median  line  (Fig.  138)  exposing  the  entire  ventral 
aspect  of  the  right  kidney  and  the  inferior  vena  cava  beneath  the 
primary  lumbar  parietal  peritoneum.  This  manipulation  will 
also  expose  the  dorsal  surface  of  the  head  of  the  pancreas,  covered 
by  what  originally  was  the  right  leaf  of  the  mesoduodenum. 

Fig.  140  indicates  the  results  of  adhesion  of  the  duodenum, 
pancreas  and  mesoduodenum  to  the  parietal  peritoneum  as  it 
normally  occurs  in  the  human  subject.  It  will  be  seen  that 
the  primary  parietal  peritoneum  can  be  traced  mesad  over  the 
ventral  surface  of  the  right  kidney  as  far  as  the  point  X,  and 
that  from  here  on  to  the  median  line  the  peritoneum  is  sec- 
ondary parietal  peritoneum,  consisting  of  the  visceral  peritoneal 
investment  of  the  ventral  surface  of  the  duodenum  and  of  the 
original  left  leaf  of  the  mesoduodenum,  beneath  which  the  ven- 
tral surface  of  the  pancreas  is  seen.  Pancreas  and  duodenum 
occupy  in  the  adult  secondarily  a  "retro-peritoneal"  position,  i.  e., 
the  peritoneum  now  covering  the  ventral  surface  of  these  viscera 
appears  as  a  continuation  of  the  parietal  peritoneum,  the  transi- 
tion between  primary  and  secondary  parietal  peritoneum  occur- 
ring along  the  line  marked  X  in  Fig.  140.  The  opposed  peri- 
toneal surfaces  indicated  by  the  dotted  lines  have  become  adher- 
ent and  converted  into  loose  connective  tissue  in  which  the 
pancreas  and  duodenum  lie  imbedded.  In  the  human  embryo 
this  process  of  adhesion  begins  in  the  eighth  week,  starting  at  the 
duodeno-jejunal  flexure  and  ascending  gradually  toward  the 
pylorus.     At  the  end  of  the  fourth  month  the  union  is  complete. 

^  The  student  should  not  be  confused  by  the  fact  that  a  considerable  portion  of  the  pan- 
creatic gland  in  the  cat  will  be  found  included  between  the  layers  of  the  great  omentum,  ex- 
tending over  to  the  left  aide  of  the  abdomen.  This  circumstance  will  be  found  of  importance 
in  studying  the  development  of  the  dorsal  mesogastrium  and  of  the  structures  connected  with 
it.  For  the  present  attention  should  only  be  given  to  the  right  extremity  or  head  of  the 
XKtncreas,  situated  close  to  the  duodenum  and  included  between  the  layers  of  the  mesoduo- 
denum. 


72  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

Proceeding  caudad  it  will  next  be  observed  that  the  peritoneum 
of  the  mesentery  occupies  the  narrow  neck  of  the  duodeno- colic 
isthmus,  and  that  large  vessels  (the  superior  mesenteric)  pass  be- 
tween its  two  layers  at  this  point  to  supply  the  segments  of  the 
intestine  forming  the  loop.  In  conformity  with  the  greatly  in- 
creased length  of  the  intestine  it  will  be  found  that  the  mesen- 
tery expands  from  the  narrow  pedicle  at  the  neck  in  a  fan-shaped 
manner  in  order  to  develop  a  sufficiently  long  margin  for  attach- 
ment to  the  intestine.  The  following  points  should  be  carefully 
borne  in  mind  in  studying  the  mesentery  with  the  intestines  in 
this  position : 

1.  The  mesentery  presents  two  free  surfaces,  right  and  left. 
With  the  coils  of  the  small  intestine  turned  over  to  the  right,  the 
left  leaf  of  the  mesentery  is  turned  toward  the  observer. 

2.  Inasmuch  as  the  descending  limb  of  the  embryonic  loop  has 
developed  the  greater  part  of  the  small  intestine,  while  a  portion 
of  the  large  intestine  (caecum  and  colon  up  to  the  isthmus)  is  the 
result  of  differentiation  within  the  ascending  or  returning  limb  of 
the  loop,  it  will  be  at  once  apparent  that  the  double  peritoneal 
layer  which  extends  between  the  duodeno-colic  isthmus  and  the 
attached  border  of  the  gut  is  partly  mesentery  of  the  small  in- 
testine, partly  mesocolon  passing  to  the  large  intestine  (csecum 
and  proximal  colon).  This  condition  may  be  indicated  schemat- 
ically in  Fig.  141. 

The  curved  line  A  may  be  taken  as  an  arbitrary  division  between 
the  portion  of  the  membrane  which  on  the  right  of  the  figure 
passes  to  the  small  intestine,  and  the  portion  which  proceeds  to 
the  left  to  be  attached  to  the  large  intestine.  In  other  words  the 
line  will  schematically  separate  the  true  mesenteric  from  the  meso- 
colic  segment  of  the  primitive  membrane. 

With  the  parts  in  their  present  position  this  line  might  be  as- 
sumed to  indicate  a  strip  along  which  the  opposed  serous  surfaces 
of  the  parietal  peritoneum  and  the  right  leaf  of  the  primitive 
mesentery  became  adherent.  In  that  case  an  actual  division  into 
a  mesenteric  and  meso-colic  segment  would  have  been  effected. 


PLATE    LXV. 


DUODENUM 


HEAD    OF 

PANCREAS, 

BETWEEN 

LAYERS  OF 

MCSODUO- 

DENUM 

AORTA 

PRIMITIVE 

PARIETAL 

PERITONEUM 


L.    KIDNEY 


POSTCAVA 
PRIMITIVE 
PARIETAL 
PERITONEUM 


R.   KIDNEY 


Figs.  138-140. — Diagrammatic  representation  of  three  stages  in  the  development  of  the  meso- 
duodenum,  duodenum,  and  pancreas  leading  to  the  secondary  "retroperitoneal"  position  of  these 
viscera. 

Fig.  138. — Free  mesoduodennm  in  sagittal  ijlane,  including  head  of  pancreas  between  right 
and  left  layers. 


VENTRAL  (original    LEFT) 
LAYER    OF    MESODUODENUM 
PANCREAS 

DUODENUM 

DORSAL   (ORIGINAL    RIGHT) 

LAYER  OF  MESODUODENUM 


PRIMITIVE 

PARIETAL 

PEHIT 


L.    KIDNEY 


POSTCAVA 

PRIMITIVE     PARIETAL 
PERITONEUM 

R.    KIDNEY 


Fig.   139. — Mesoduodeuum  folded  to   right;    left  leaf   has  become  ventral;  right  dorsal, 
directed  toward  primitive  prerenal  parietal  peritoneum. 


SECONDARY  PARIETAL 
PER  IT.  COVERING  VEN- 
TRAL SUR  FACE  O  F  PAN- 
CREAS DERIVED  FROM 
LEFT  LAYER  OF  MESO- 
DUODENUM 
DUODENUM 

POSTCAVA 

X.SECONDARY  TRANSI- 
TION FR.  VISCERAL  TO 
PARIETAL  PERITONEUM 

KIDNEY 


AREA  OF  ADHESION  BETWEEN  RIGHT  SUB- 
SEQUENTLY DORSAL)  LAYER  OF  MESODUO- 
DENUM AND  PRIMITIVE  PARIETAL  PERI- 
TONEUM 


Fig.  140. — Fixation  of  head  of  pancreas  and  duodenum  under  cover  of  secondary 
parietal  peritoneum  by  adhesion  of  apposed  surfaces  of  mesoduodennm  and  primitive 
parietal  peritoneum. 


PLATE    LXVI. 


DUODENOCOLIC 
ISTHMUS 


SEGMENT  OF  PRIMI- 
TrVE  COMMON  MES- 
ENTERY OF  INTESTI- 
NAL LOOP  PRODUC- 
ING MESENTERY  OF 
JEJUNO-ILEUM 


DORSAL    MESO- 
GASTRIUM 


MESODUODENUM 

SEGMENT     OF     PRIM- 
ITIVE  COMMON    MES- 
ENTERY   OF    INTESTI- 
NAL      LOOP      FROM 
WHICH    ASCENDING 
AND     TRANSVERSE 
MESOCOLA    ARE    DE- 
RIVED 

DISTAL  PORTION  OF 
PRIMITIVE  COMMON 
DORSAL  MESENTERY 
FURNISHING  MESO- 
COLA OF  DESCEND- 
ING COLON  AND 
OMEGA     LOOP 


Fig.  141. — Schematic  representation  of  mesentery  of  umbilical  loop,  common  to  small 
intestine  and  proximal  portion  of  large  intestine. 


DIVIDED    VENTRAL 
MESOGASTRIUM 


STOMACH 


DORSAL 
MESOGASTRIUM 


INTESTINE 


Figs.  142-144.— Scliematic  representation  of  three  stages  in  the  development 
of  the  mesentery  of  the  umbilical  intestinal  loop. 

Fig.  142.— Early  stage  before  differentiation  of  intestinal  canal. 


PLATE    LXVII. 


DIVIDED 
VENTRAL 
MESOGAS- 
TRIUM 


DUODENUM 


DESCENDING 
LIMB    OF 
INTESTINAL 
LOOP 

mesentery 
'primitive^ 

VITELLO- 
INTESTINAL 
DUCT 


STOMACH 


DORSAL   MESO* 
GASTRIUM 


MESODUODENUM 


ASCENDING 
LIMB    OF 
INTESTINAL 
LOOP 


TERMINAL 
SEGMENT 
OF  COLON 


Fig.  143. — Stage  of  umbilical  loop.  Difl'erentiation  of  common  dorsal 
mesentery  of  earlier  stage  into  dorsal  mesogastrium,  mesoduodenum,  primitive 
mesentery  of  umbilical  loop,  and  descending  mesocolon. 


DIVIDED 

ventral 

MESOGAS- 
TRIUM 


duodenum 


COMMON  PERI- 
TONEAL PLATE 
OF  MESENTERY 
AND  ASCEND 
iNG  AND  TRANS 
VERSE  MESO 
COLON 


DORSAL 
MESOGAS- 
TRIUM 


MESODUODENUM 


ASCENDING 
COLON 


DESCENDING 
COLON 


P'iG.  144. — Final  stage.  With  complete  diflerentiation  of  large  and  small 
intestine,  the  primitive  mesentery  of  the  umbilical  loop  contains  not  only  the 
mesentery  of  the  future  jejuuo-ileum,  but  also  the  mesocola  and  the  ascending 
and  transver.se  colon,  developed  from  the  ascending  or  afferent  limb  of  the  um- 
bilical loop. 


> 


PLATE   LXIX. 


STOMACH 


DUODENO- 
JEJUNAL 
JUNCTION 


Fig.  147. — Human  foetus,  6.6  cm.,  vertex-coccygeal  measure  ;  liver 
removed,     (Columbia  University  Museum,  Study  Collection.)    X  4. 


POSTCAVA 

RIGHT   ADRENAL 

SUPRACOLIC    PART 

OF    DUODENUM 

RIGHT    KIDNEY 

COLON    (A) 

TERMINAL 
ILEUM 

RIGHT    OVARY 


SSCPHAGUS 


STOMACH 

LESSER    CURVATURE 
PORTAL   VEIN 
PYLORUS 

SPLENIC    FLEXURE 
OF   COLON    (B) 

/ 
3D    PART    OF    DUO- 
DENUM 

DESCENDING 
COLON 

OMEGA    LOOP 


Fig.  148.  — Abdominal  viscera  of  human  foetus  of  12.5  cm.,  vertex-coccygeal 
measure,  hardened  in  situ;  transverse  and  ascending  colon  not  yet  differen- 
tiated.    (Columbia  University  Museum,  No.  1815.)     Natural  size. 


PLATE    LXX. 


HEPATIC 

FLEXURE 

OF    COLON 


ASCENDING 
COLON 


TERMINAL 
ILEUM 


STOMACH 
SPLEEN 


TRANSVERSE 
COLON 


Fig.  149. — Abdominal  viscera  of  human  foetus  at  term,  hardened 
in  situ;  hepatic  flexure  formed  and  ascending  and  transverse  colon 
differentiated.      (Columbia  University  Museum,    No.  1816.) 


UMBILICAL 
CORD 


ALLANTOIC 
DUCT 


WOLFFIAN 
DUCT 


VITELLINE 

DUCT 
MID-GUT 


WOLFFIAN 
BODY 


WOLFFIAN 
DUCT 


Fig.  150. — Caudal  portion  of  human  embryo  of  5  mm.,  with  the 
end-  and  caudal  gut  at  the  highest  stage  of  its  development.  X  25. 
(Eeconstruction  after  His.) 


PLATE    LXXI. 


HEPATIC 

FLEXURE 

OF   COLON 


GREAT   OMENTUM 
TURTLE  O-UP 


TRANSVERSE 
MESOCOuON 
COVERING 
COILS    OF 
SMALL    IN- 
TESTINE 


TRANSV.    COLON 
BENT    IN    V-SHAPE 
TO    PUBES 


Fig.  1")!. — Abdominal  viscera  of  Macacus  rhesus,  rhesus  monkey,  hard- 
ened m  situ.     (Columbia  University  Museum,  No.  1817.) 


VISCERAL 
PERIT.  OF 
DESCEND- 
ING DUO- 
DENUM 


DUODENUM 


Figs.  l.')2-l.'J4. — Schematic  representaticni  of  peritoneum  in 
fixation  of  descending  duodenum  and  formation  of  transverse 
colon  and  mesocolon. 

Fig.  152. — Sagittal  section  through  right  kidney  and 
descending  duodenum  before  adhesion  of  latter  to  parietal 
peritoneum. 


PLATE    LXXII. 


ADHESION  BETW.  PRIMITIVE 
PARIETAL  PERIT.  AND  DOR- 
SAL VISCERAL  SEROSA  OF 
DUODENUM 


R.    KIDNEY 


TRANSITION  OF  PRIMITIVE 
INTO  SECONDARY  PARIETAL 
PERITONEUM  DERIVED  FROM 
VENTRAL  VISCERAL  SEROSA 
OF    DUODENUM 


PARIETAL 
PERITONEUM 


VENTRAL    VISCERAL    SEROSA 
OF      DUODENUM       FORMING 
SECONDARY       PARIETAL 
PERITONEUM 

DESCENDING    DUODENUM 


LAYERS    OF    MESOCOLON 


Fig.  153.— Adhesion  of  descending  duodenum  to  primitive  parietal  peritoneum, 
mesocolon  after  rotation  of  the  intestine,  but  before  adhesion. 


Colon  and 


ADHESION    BETWEEN 
PRIMITIVE  PARIETAL 

PERITONEUM  AND 
DORSAL  .VISCERAL 
SEROSAOF   DUODENUM 


POINT  WHERE  MESO- 
COLON BEGINS  TO  RE- 
PLACE PRIMITIVE  PRE- 
RENAL PARIETAL  PERI- 
TONEUM 

ADHESION    BETWEEN 
PRIMITIVE  PARIETAL 

PERIT.  AND  DORSAL 
LAYER   OF    MESOCOLON 


VENTRAL  VISCERAL  SEROSA 
OF  DUODENUM  FORMING  SEC- 
ONDARY PARIETAL  PERITO- 
NEUM COVERING  SUPRACOLIC 
PORTION    OF    DUODENUM 


HEPATIC    FLEXURE    OF    COLON 


beginning  oftransv.  colon 
secondary  parietal  perit. 
derived  from  mesocolon 
covering  infracolic  seg- 
ment of  duodenum 
area  of  adhesion  between 
mesocolon  and  visceral 
serosa  of  duodenum 

secondary    parietal  perit. 
(mesocolic)     covering     R. 

KIDNEY 


Fig.  154. — Adhesion  of  mesocolon  to  duodenum  and  primitive  parietal  peritoneum,  resulting 
in  formation  of  root  of  transverse  mesocolon. 


PRIMITIVE  MESENTERY  OF   UMBILICAL  LOOP.  73 

Ventrad  and  to  the  right  of  this  line  of  adhesion  we  would  trace 
that  portion  of  the  primitive  membrane  which  now  passes  to  the 
coils  of  the  small  intestine  as  the  true  mesentery,  having  an  ap- 
parent origin  in  the  background  of  the  abdomen  to  the  dotted  line 
of  adhesion.  In  the  same  manner  the  peritoneal  layers  passing 
to  the  left  to  reach  the  caecum  and  beginning  of  the  colon  would 
appear  as  a  free  meso-colon  with  the  same  line  of  apparent  origin 
from  the  background  of  the  abdomen.     (Cf.  p.  80.) 

These  considerations  should  be  followed  out  in  the  dissection  of 
the  cat  in  order  to  become  familiar  with  the  principle  of  secondary 
lines  of  origin  for  peritoneal  layers.  As  we  will  see  later  this  fac- 
tor is  of  importance  in  correctly  estimating  the  value  of  the  human 
adult  conditions. 

3.  A  brief  consideration  of  the  mechanical  conditions  and  com- 
parison with  the  earlier  stages  will  show  why  the  peritoneal  layers 
which  occupy  the  bight  of  the  fully  developed  umbilical  loop  are 
especially  prone  to  develop  secondary  lines  and  areas  of  adhesion 
to  other  serous  surfaces.  If  we  compare  the  dorsal  mesentery  in 
its  primitive  condition,  before  the  straight  intestinal  tube  has  be- 
come differentiated  into  the  subsequent  segments,  and  before  the 
umbilical  loop  has  been  formed  (Fig.  142),  with  the  later  stages 
represented  by  the  intestines  of  the  cat  as  now  arranged  (Figs. 
143  and  144),  it  will  be  seen  that  the  vertical  line  of  attachment 
to  the  ventral  surface  of  the  vertebral  column,  between  the  points 
a  and  b  corresponds  in  the  advanced  stages  to  the  interval  ab 
separating  the  two  points  of  the  duodeno-colic  isthmus  ;  also  that 
the  entire  mesenteric  peritoneal  surface  beyond  the  isthmus  is  the 
result  of  drawing  out  and  lengthening  the  intestinal  tract.  Con- 
sequently folding  or  overlapping  of  this  extensive  membrane 
affords  opportunities  for  adhesions  between  its  own  serous  surfaces 
or  between  it  and  the  remaining  visceral  and  parietal  peritoneum 
of  the  abdomen. 

Moreover,  it  will  be  appreciated  that  the  entire  extensive  coil 
of  intestines  extending  between  the  two  boundaries  of  the  duodeno- 
colic  isthmus  (a,  b)  is  suspended  from  the  back  part  of  the  abdo- 


74  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

men  by  a  narrow  pedicle  and  that  consequently  rotation  will 
readily  occur  around  the  axis  drawn  through  the  neck  of  the 
isthmus. 

Now  proceed  to  illustrate  on  the  cat  the  result  of  the  rotation 
as  it  occurs  normally  during  the  development  of  the  primate  in- 
testinal tract.  Take  the  caecum  and  commencement  of  the  colon 
and  draw  the  same  over  to  the  right  across  the  duodeno-colic 
isthmus  and  the  duodenum.  Twist  or  rotate  the  entire  mass  of 
small  intestines  around  the  isthmic  pedicle,  so  that  the  original  left 
leaf  of  the  mesentery  will  look  to  the  right  and  vice  versa  (Fig. 
145).  The  conditions  thus  established  will  be  found  to  correspond 
to  the  schemata  shown  in  Figs.  114  and  115.  The  main  features 
of  the  intestinal  tract  in  the  rearranged  position  will  be  as  follows  : 

1.  The  two  points,  a  and  6,  of  the  duodeno-colic  isthmus  (Fig. 
145)  are  still  close  together,  but  reversed  in  position,  h  is  in  front 
and  to  the  right,  a  behind  and  to  the  left,  whereas  before  the  rota- 
tion h  was  situated  below  and  to  the  left,  a  above  and  to  the  right 
(Fig.  135). 

2.  The  direction  of  the  ileo-colic  entrance  is  reversed,  the  ileum 
now  entering  the  large  intestine  from  below  and  the  left  upwards 
and  to  the  right,  instead  of  from  right  to  left. 

3.  The  descending  duodenum  is  now  situated  dorsad  to  the  colon. 

4.  The  original  left  leaf  of  the  mesentery  has  become  the  right, 
and  vice  versa. 

5.  The  superior  mesenteric  artery  crosses  over  the  transverse 
portion  of  the  duodenum,  and  with  the  exception  of  the  inferior 
pancreatico-duodenal  artery  the  original  right-sided  branches  now 
arise  from  the  left  side  of  the  vessel  and  v'we  versa. 

It  is  now  time  to  compare  the  conditions  established  in  the  cat 
by  the  manipulations  just  detailed  with  the  arrangement  of  the 
adult  human  intestinal  tract  and  peritoneum  below  the  level  of 
the  transverse  colon  and  mesocolon. 

I.  The  shortness  of  the  large  intestine  in  the  cat  will  require 
careful  manipulation  in  order  to  produce  a  disposition  in  con- 
formity with  the  arrangement  of  this  portion  of  the  human  intes- 


RELATIONS  OF  COLON.  76 

tinal  tract.  By  stretching  the  gut  somewhat  and  pulling  it  well 
out  of  the  pelvis  sufficient  length  will  be  obtained  to  establish  an 
ascending,  transverse  and  descending  colon.  Move  the  caecum 
from  the  subhepatic  position  which  it  occupies  immediately  after 
rotation  (Fig.  145)  down  to  the  lower  and  right-hand  corner  of 
the  abdomen.  Pull  the  distal  portion  of  the  large  intestine  well 
out  of  the  pelvis  and  obtain  thus  sufficient  length  to  establish 
an  ascending,  transverse  and  descending  division  each  provided 
with  a  free  mesocolon  (Fig.  146).  In  the  formation  of  the  three 
definite  main  segments  of  the  human  large  intestine,  ascending, 
transverse  and  descending  colon,  the  following  stages  may  be 
recognized : 

1.  Immediately  after  rotation  the  large  intestine  lies  trans- 
versely along  the  greater  curvature  of  the  stomach,  with  the 
caecum  on  the  nght  side  in  front  of  the  duodenum  and  closely 
applied  to  the  caudal  surface  of  the  right  lobe  of  the  liver  (Fig. 
147). 

Persistence  of  Subhepatic  Position  of  CiEcuM  in  Adult. — 
The  period  at  which  thje  caecum  descends  into  the  iliac  fossa  is 
liable  to  a  considerable  range  of  variation. 

Treves  found  in  two  foetus,  measuring  respectively  4  J"  and  5  J", 
the  caecum  on  a  level  with  the  caudal  end  of  the  right  kidney, 
while  in  several  individuals  at  full  term  the  caput  coli  was  still 
placed  immediately  below  the  liver,  with  no  large  intestine  in  the 
place  of  the  ascending  colon.  This  condition  is  well  illustrated 
in  the  foetus  shown  in  Fig.  124. 

The  caecum  may  remain  undescended  throughout  life.  Treves, 
in  an  examination  of  100  bodies,  found  this  condition  in  two  sub- 
jects, both  females,  one  41,  the  other  74  years  of  age.  Both  cases 
presented  an  identical  disposition.  There  was  no  large  intestine 
in  the  place  of  the  ascending  colon.  The  caecum  was  placed  on 
the  right  side,  immediately  underneath  the  Uver,  just  to  the  right 
of  the  gall-bladder ;  it  was  quite  horizontal  in  position,  continu- 
ing the  long  axis  of  the  transverse  colon  and  included  between 
the  layers  of  the  transverse  mesocolon.     From  the  extremity  of 


76  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

the  csecum  a  horizontal  fold  was  continued  to  the  abdominal 
parietes  and  upon  it  the  edge  of  the  liver  rested.  In  one  of  these 
instances  the  colon  from  the  tip  of  the  cascum  to  the  splenic 
flexure  measured  38".  The  great  omentum  was  attached  only  to 
the  left  half  of  this  portion.  The  descending  colon  was  very  long, 
measuring  15". 

In  the  other  case  the  distance  from  the  tip  of  the  caecum  to  the 
splenic  flexure  was  27",  the  great  omentum  commencing  5"  from 
the  former  point.     The  descending  colon  was  of  normal  length. 

In  both  bodies  the  remaining  viscera  were  normal. 

2.  The  caecum  next  descends  ventrad  of  right  kidney  to  the 
iliac  fossa.  The  future  ascending  colon  is  at  this  time  placed  very 
obliquely  on  account  of  the  large  size  of  the  foetal  liver,  and  passes 
without  a  marked  angle  into  the  transverse  segment.  Thus  in 
Fig.  148,  from  a  foetus  5"  in  length,  the  descending  colon  is  verti- 
cal and  the  splenic  flexure  well  marked,  forming  the  highest  point 
of  the  colic  arch.  There  is  no  hepatic  flexure,  and  no  ascending 
and  transverse  colon,  but  instead  of  these  an  oblique  segment  pass- 
ing upwards  and  to  the  left  between  caecum  and  splenic  flexure. 

This  disposition,  due  to  the  large  size  of  the  liver,  is  still  marked 
at  times  in  the  foetus  at  term,  and  occasionally  even  in  children 
np  to  2  or  3  years  of  age. 

3.  The  ascending  colon  is  subsequently  differentiated  from  the 
transverse  segment  and  the  hepatic  flexure  formed  consequent 
upon  the  diminution  of  the  relative  size  of  the  liver,  which  per- 
mits the  foetal  oblique  segment  of  the  colon  extending  in  the 
earlier  stages  between  the  right  iliac  fossa  and  the  spleen  to  be- 
come divided  by  a  right-angled  (hepatic)  bend  or  flexure  into  an 
ascending  and  a  transverse  segment  (Fig.  149). 

4.  The  splenic  flexure  develops  early  and  is  well  marked.  It 
indicates  the  point  of  transition  of  the  original  ascending  limb 
of  the  umbilical  loop  into  the  remaining  vertical  median  segment 
of  the  large  intestine,  from  which  the  descending  colon  is  formed. 

In  the  adult  the  ascending  and  descending  portions  of  the 
colon  are  vertical.     The  transverse  colon  is  not  quite  horizontal 


DIFFERENTIATION  OF  ASCENDING  AND  TRANSVERSE  COLON.        77 

since  the  splenic  flexure  is  higher  and  placed  more  dorsally  than 
the  hepatic  flexure.  In  the  embryo  the  rapidly-growing  coils  of 
the  small  intestine  push  the  descending  colon  to  the  left  and 
dorsad  into  close  contact  with  the  dorsal  abdominal  wall. 

A  small  bend  which  appears  about  the  middle  of^the  third 
month  in  the  left  iliac  fossa  indicates  the  rudiment  of  the  future 
sigmoid  flexure  or  omega  loop. 

The  rest  of  the  endgut  follows  the  body  wall  in  a  well-marked 
curve,  whose  termination  lies  within  the  concavity  of  the  caudal 
portion  of  the  embryo  (Fig.  150).  From  this  terminal  part  the 
rectum  develops  after  the  division  of  the  cloaca  and  the  union  of 
the  proctodseum  with  the  entodermal  intestinal  pouch  has  taken 
place  as  detailed  above. 

The  early  position  of  the  colon  produced  by  the  large  size  of 
the  foetal  liver,  and  before  the  descent  of  the  caecum  has  occurred, 
is  shown  in  Fig.  124.  In  Fig.  123,  where  the  liver  has  regained 
its  normal  proportions  with  reference  to  the  abdominal  cavity  and 
viscera,  and  the  caecum  has  descended  into  the  right  iliac  fossa, 
the  hepatic  flexure  is  well  marked  and  the  first  segment  of  the 
colon  has  acquired  the  vertical  position  on  the  right  side,  the 
single  obliquely  transverse  segment  of  Fig.  124,  having  become 
divided  into  an  ascending  and  a  transverse  colon. 

[Fig.  124.  Early  stage.  Liver  relatively  large.  Proximal 
portion  of  the  colon  extends  obliquely  between  the  right  lumbar 
region  and  the  spleen.     The  caecum  has  not  yet  descended. 

Fig.  123.  Later  stage.  The  caecum  occupies  the  right  iliac 
fossa.  Relative  reduction  in  the  size  of  the  liver  allows  the  colic 
segment  to  be  divided  by  the  hepatic  flexure  into  an  ascending 
colon  and  a  transverse  colon.] 

At  times  the  transverse  colon,  whose  normal  average  length  in 
the  adult  is  20",  greatly  exceeds  this  measurement  and  forms  an 
arch  which  hangs  down  or  makes  a  well-marked  V-shaped  bend 
with  the  apex  directed  toward  the  pubes.  This  is  the  normal 
arrangement  of  this  portion  of  the  large  intestine  in  many  of 
the  lower  primates.      Fig.  151  shows  the  abdominal  viscera  of 


78  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

Macacus  rhesus,  hardened  in  situ,  seen  from  the  front  and  the 
right  side,  with  the  omentum  turned  up  over  the  stomach.  The 
transverse  colon  forms  an  extensive  V-shaped  bend,  whose 
apex  reaches  to  the  pubes,  from  which  point  the  large  intestine 
turns  again  cephalad  and  dorsad  to  form  the  splenic  flexure  and 
then  descends  to  the  pelvis. 

The  average  length  of  the  ascending  colon  in  the  adult,  meas- 
ured from  the  tip  of  the  caecum  to  the  hepatic  flexure,  was  found 
by  Treves  in  his  series  of  100  bodies  to  be  8",  while  the  descend- 
ing colon,  from  the  splenic  flexure  to  the  beginning  of  the  sigmoid 
loop,  measured  8i". 

The  descending  colon  may  at  times  be  much  longer,  up  to  15", 
and  become  convoluted. 

II.  In  the  next  place,  in  order  to  understand  the  arrangement 
of  the  peritoneum  in  this  lower  larger  compartment  of  the  abdo- 
men, disregard  for  the  present  the  peritoneal  connections  of  the 
stomach,  liver,  pancreas  and  spleen,  and  the  folds  of  the  great 
omentum  entirely.  This  latter  membrane  is  adherent  in  the 
adult  human  subject  by  its  dorsal  surface  to  the  upper  margin  of 
the  transverse  colon,  so  that  in  turning  the  omentum  up  over 
the  ventral  chest  wall  the  transverse  colon  will  be  carried  with 
the  omentum  and  the  lower  layer  of  the  transverse  mesocolon 
will  be  put  upon  the  stretch.  This  membrane  forms  in  adult  man 
by  its  transverse  attachment  to  the  abdominal  backgi-ound  the 
cephalic  limit  of  the  larger  lower  compartment  of  the  abdomen, 
which  is  framed  laterally  by  ascending  and  descending  colon,  con- 
tinuous below  with  the  pelvic  cavity  and  occupied  chiefly  by  the 
freely  movable  coils  of  the  jejuno-ileum. 

Remember  that  the  duodenum  starting  from  the  pyloric  ex- 
tremity of  the  stomach  first  turns  cephalad  and  dorsad  in  contact 
with  the  caudal  surface  of  the  right  lobe  of  the  liver,  forming  the 
first  portion  or  hepatic  angle  of  the  duodenum  ;  that  in  the  next 
place  the  second  or  descending  portion  of  the  duodenum  passes 
down  in  front  of  the  medial  part  of  the  ventral  surface  of  the 
right  kidney  and  the  inferior  vena  cava,  but  behind  the  right  ex- 


COURSE  OF  DUODENUM,  THE  MESOCOLA   AND  THE  MESENTERY.     79 

tremity  (hepatic  flexure)  of  what  after  rotation  and  formation  of 
the  ascending  colon  appears  as  the  transverse  colon ;  that  conse- 
quently the  descending  duodenum  is  divided  by  its  intersection, 
with  the  transverse  colon  into  a  cephalic  supra-colic  and  a  caudal 
infra-colic  segment. 

Also  remember  that  the  second  angle  of  the  duodenum  (transi- 
tion between  the  descending  and  transverse  portions)  is  conse- 
quently situated  to  the  right  of  the  vertebral  column  below  the 
level  of  the  transverse  colon  and  the  secondary  attachment  pres- 
ently to  be  considered  of  the  transverse  mesocolon  to  the  back- 
ground of  the  abdominal  cavity. 

The  third  portion  of  the  duodenum  extends  from  this  point 
more  or  less  transversely — depending  upon  the  type — to  the  left, 
across  the  vertebral  column  and  aorta.  This  transverse  portion, 
after  the  rotation  of  the  primitive  loop  at  the  duodeno-colic  angle, 
is  crossed  in  the  direction  caudad  and  ventrad  by  the  superior 
mesenteric  vessels,  which  hence  divide  this  portion  of  the  intes- 
tine into  a  right  and  left  segment. 

The  latter  turns  cephalad  and  ventrad  on  the  left  side  of  the 
vertebral  column  (4th  or  ascending  portion)  to  become  continuous 
at  the  duodeno-jejunal  angle  with  the  free  or  floating  small  intes- 
tine (jejunum). 

If  we  imagine  in  the  cat  the  duodenum  anchored  or  fixed  by 
adhesion  of  the  dorsal  (originally  right)  leaf  of  the  mesoduode- 
num  and  of  its  own  dorsal  visceral  peritoneum  to  the  abdominal 
parietal  peritoneum  in  the  manner  above  indicated  (p.  70)  as 
far  as  the  duodeno-jejunal  angle  we  will  have  conditions  estab- 
lished which  correspond  to  those  found  in  the  human  adult  ab- 
dominal cavity. 

III.  It  is  next  necessary  to  study  carefully  the  disposition  of  the 
primitive  dorsal  mesentery  connected  after  rotation  with  the  dif- 
ferent segments  of  the  intestinal  tube,  ascending,  transverse  and 
descending  colon  and  free  small  intestine. 

In  order  to  obtain  in  the  cat  a  cephalic  limit  to  the  region  now 
under  consideration  which  will  correspond  to  the  arrangement  of 


80  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

the  adult  human  peritoneum,  we  will  begin  with  the  peritoneal 
membrane  attached  to  the  portion  of  the  colon  which  in  the  re- 
arranged intestinal  tract  represents  the  human  transverse  colon. 
This  transverse  segment  of  the  large  intestine  is  now  made  to  ex- 
tend directly  across  the  abdomen  from  the  liver  to  the  spleen. 
The  two  layers  composing  the  transverse  mesocolon  are  an  upper 
or  cephalic  and  a  lower  or  caudal  layer. 

Now  it  will  be  seen  in  the  cat  that  the  upper  or  cephalic  layer 
of  the  transverse  mesocolon  thus  established^  is  continuous  on 
each  side  with  the  dorsal  (originally  right)  leaf  of  the  ascending 
and  with  the  dorsal  (originally  left)  leaf  of  the  descending  meso- 
colon, which  peritoneal  layers  are  in  direct  opposition  to  the 
parietal  lumbar  and  prerenal  peritoneum.  On  the  other  hand, 
the  inferior  or  ventral  layer  of  the  transverse  mesocolon  is  con- 
tinuous on  each  side  of  the  median  line  with  the  ventral  (origi- 
nally respectively  left  and  right)  leaves  of  the  same  mesocola, 
while  at  the  site  of  the  duodeno-colic  isthmus  the  two  layers  of 
the  transverse  mesocolon  are  continuous  as  originally  with  the 
two  layers  of  the  mesentery  of  the  jejuno-ileum  (Fig.  146). 

Now  fix  the  transverse  mesocolon  firmly  against  the  back- 
ground of  the  abdomen  and  place  the  ascending  and  descending 
colon  as  far  as  possible  over  to  the  right  and  left  side  respectively. 
We  will  assume  a  line  of  secondary  adhesion  between  the  trans- 
verse mesocolon  and  the  parietal  peritoneum  investing  the  dorsal 
abdominal  wall.  Along  this  line  the  upper  or  cephalic  surface  of 
the  transverse  mesocolon  would  become  continuous  with  the  dorsal 
parietal  peritoneum,  while  the  lower  or  caudal  layer  would  still 
be  continuous  with  the  left  leaf  of  the  ascending  and  the  right 
leaf  of  the  descending  mesocolon.  We  have  already  seen  that  the 
duodenum  and  mesoduodenum  become  anchored  in  the  sub- 
hepatic region  and  that  the  visceral  ventral  peritoneum  of  the 
gut  and  the  original  left  leaf  of  the  mesoduodenum  appear  then 
as  secondary  parietal  peritoneum.  Hence  a  sagittal  section 
through  the  right  lumbar  region,  right  kidney  and  descending 
duodenum  would,  immediately  after  rotation  and  establishment 


PLATE    LXXIII. 


GREAT 

OMENTUM 

RAISED 


HEPATIC 

FLEXURE 

OF    COLON 

TRANSVERSE 
COLON 


PANCREAS 


L.    KIDNEY 

FREE    DE- 
SCENDING 
MESOCOLON 


Fig.  155. — Abdominal  viscera  of  Macacus  cynomolgiis,  Kra  monkey,  liardened  in  situ.    (Colum- 
bia University  Museum,  No.  1801.) 


PLATE    LXXIV 


NON-PERITONEAL 
SURFACE  OF  RIGHT 
ADRENAL  ADHER- 
ENT   TO    LIVER 

PERITONEAL  SUR- 
FACE OF  RIGHT  AD- 


PERITONEAL  (he 
PATIC)  AREA  OF  R 
KIDNEY 


COLON    AT    HE- 
PATIC   FLEXURE 

PERITONEAL  (meSO- 
COLIC)  AREA  OF  R. 
KIDNEY 


DESCENDING 
DUODENUM 


TRANSVERSE 
MESOCOLON 


Fig.  156. — Schema  of  visceral  and  peritoneal  relations  of  ventral  sur- 
face of  right  Itidney. 


DESC.  COLON 


DESC. 
MESOCOLON 


PRIMARY    PARIE- 
TAL   PERIT. 


t 

T 

S^ 

SMALL 
NTESTINE 


MESENTERY 


ASC.    COLON 


ASC.   MESO- 
COLON 

PRIMARY 
PARIETAL 
PERIT. 


Fig.  157. 


SECOrlDARY 
PARIETAL 
PERIT.    FROM 
R.     LAYER 
DESC.    MESO- 
COLON 

DESC.  COLON 
AREA  OF  ADHESION 
BETW.  L.  LAYER  DESC. 
MESOCOLON  AND  PRI- 
MARY PARIETAL  PERIT. 
L.    KIDNEY 


c 

=^ 

S 

r 

Ka/' 

SMALL 
INTESTINE 

MESENTERY 

SECONDARY    PARIETA5- 
PERIT.    FROM      LEFT 
LAYER    OF   ASC. 
MESOCOLON 


ASC.    COLON 

AREA    OF    ADHESION    BETW      R 
LAYER  ASC.    MESOCOLON     AND 
PRIMARY    PARIETAL    PER'T 
R.    KIDNEY 


Fig.  158. 

Figs.  157,  158. — Schema  showing  peritoneal  arrangement  in  transection  of  infracolic  compart- 
ment of  abdomen  before  and  after  fixation  of  ascending  and  descending  colon. 


PLATE    LXXV. 


R.    KIDNEY 

DUODENUM 

MESENTERY  OFJEJUNO-ILEUNI 

CROSSING  TRANSV.   DUOD. 

ASC.    COLON 

ASC.  MESOCOLON  ORIGINAL 
LEFT,  NOW  VENTRAL  LAYER 
FORMING  SECONDARY  PARIE- 
TAL   PERITONEUM 


GREAT   OMENTUM 
TURNED    UP 


TRANSVERSE 
COLON 

B  

CAUDAL    LAYER    OF 
TRANSV.    MESOCOLON 
L.    KIDNEY 

DESC.    COLON 

DESC.  MESOCOLON, 
ORIGINAL  RIGHT, 
NOW  VENTRAL 
LAYER  FORMING 

SECONDARY     PARIE- 
TAL   PERITONEUM 

C 

OMEGA    MESOCOLON 


OMEGA     LOOP 
INTERSIGMOID  FOSSA 


Fig.  159. — Schematic  figure  to  show  lines  of  mesocolic  adhesion,  formation  of  root  of  trans- 
verse mesocolon  and  root  of  mesentery  of  jejuno-ileum  in  human  subject. 


SMALL 
INTESTINE 


GREAT 
OMENTUM 
TURNED  UP 


MESOCOLON 


Fig.  160. — Abdominal  cavity  of  cat,   with   intestines  everted  and  elevated   to 
show  duodenal  fold.     (From  a  fresh  dissection.) 


PLATE    LXXVI. 


PORTAL   VEIN 


POSTCAVA 


R      KIDNEY 


DUODENAL 
FOLD 


PANCREAS 
STOMACH 

DUODENUM 


ILEO-COLIC 
JUNCTION 


Fig.  161.— Abdominal  viscera  of  Nasua  rufa,  brown  coaiti.     (From  a  fresh  dissection.) 


DUODENUM 


R      KIDNEY 


ILEO-COLIC 
JUNCTION 


STOMACH 


V  HEPATIC 

^        FLEXURE 
OF  COLON 


Fig.  162. — Abdominal  viscera  of  Hapale  vulgaris,  the  marmoset.    (Colum- 
bia University  Museum,  No.  1818.) 


PLATE    LXXVII. 


GREAT    OMENTUM 


MESOCOLON    CORRESPONDING 
TO      ASCENDING     AND    TRANS- 
VERSE   HUMAN    SEGMENTS 
DUODENAL    FOLD    BOUNDING 
SUP.    DUODENAL    FOSSA 

DESC.    MESOCOLON 
TERMINAL    PART   OF    DUOD 


DESCENDING    COLON 


Fig.    163.— Abdominal   viscera  of  cat ;  intestines  rotated  and  turned  to  the  riglat  to  show 
duodenal  fold.     (From  a  fresh  dissection.) 


DUODENUM 
PANCREAS 


I  LEO-COLIC 
JUNCTION 


OMENTUM 
TURNED  UP 


SUP.    MESENTERIC    ART 
DORSAL    MESENTERY 


LEFT    KIDNEY 

TERMINAL    PART    OF 

DUODENUM 
COLON 

DUODENAL    FOLD 


SMALL    IN- 
TESTINE   AND 
MESENTERY, 
WITH       ORIG- 
INAL     RIGHT 
LAYER  TURNED 
TO       LEFT       BY 
ROTATION     OF 
INTESTINE    AT 
DUODENO-COLIC 
ISTHMUS 


Fig.   164. — Abdominal  viscera  of  Nasua  rufa,  the  brown   coain,  snowin<^  the  position  of  the 
duodenal  fold  after  rotation  of  the  intestine.     (From  a  fresh  dissection.) 


PLATE    LXXVIII. 


DUODENO- 
JEJUNAL 
ANGLE 

INF.     MESENT. 
VEIN      IN      MAR- 
GIN      OF       FOLD 
BOUNDING 
DUODENAL 
FOSSA 


OMEGA     LOOP 


STOMACH 


PANCREAS 

CUT  END  OF 
TRANSVERSE 
COLON 


DESC.   COLON 


Fig.  165. — Abdominal  viscera  of  human  foetus  at  term,  arranged  to  show  duodenal 
folds  and  fossa.  The  jejuno-ileum,  ascending  and  transverse  colon  have  been  removed. 
(Columbia  University  Museum,  No.  1819.) 


R.    KIDNEY 

CUT    EDGE    OF 

MESENTERY 

iLEO-COLIC 
JUNCTION 


TRANSV.    COLON 


TRANSV.    MESO- 
COLON 

DUODENO-JEJUNAL 
ANGLE 

INF.    MESENT.   VEIN 

AND   ART.    COLICA 

SINISTRA 

DUODENAL   FOLD 


OMEGA     LOOP 


Fig.  166.— Abdominal  viscerii  t.l'  liuniMii   lii'ius  at   term.     (I'olumbia  Uni- 
versity Museum,  No.  1820.) 


PLATE    LXXIX. 


ASC     OUOD 
ENUM 


GREAT 
OMENTUM 


SUP.   DUOD< 
ENAL    FOLD 


INF.   MESENT.    , 
i/EIN    AND    ART. 
COLICA    SINISTRA 
INF.    DUOD- 
ENAL   FOLD 


Fig.    1(}7. — Abdominal   viscera  ui  ;i(lult  human  subject,  showing  duodenal  folds   and   fossa. 
(From  a  fresh  dissection.) 


PLATE    LXXX. 


TERMINATION 

OF  ASCENDING 

DUODENUM 


INTERMEDIATE 
DUOD.    FOLD 


GREAT 
OMENTUM 
TURNED  UP 


DUODENO- 
JEJUNAL 
OR     MCSO- 
COLIC   FOLD 


SUP.   DUOD- 
ENAL   FOLD 
INF.    MESEN- 
TERIC   V. 


INF.     DUOD- 
ENAL   FOLD 


/i:'    Fig    168.— Abdominal  viscera  of  adult  human  subject,  showing  duodenal   folds  and  fossa. 
(b  rom  a  iresn  dissection.) 


BRONCHUS 


CESOPHAGUS 


SMALL 
INTESTINE 


^.    Figs.   169,  170.— Two  front   views  of  the  entodermal  canal.     (Minot. 
after  His.)  ' 

Fig.  169.— Embryo  Sch.  1  of  His.     Fig.  170.— Embryo  Sch.  2  of  His. 


PERITONEAL  RELATIONS  OF  DESCENDING  DUODENUM  IN  ADULT.  81 

of  the  transverse  mesocolon,  show  the  peritoneal  arrangement 
indicated  in  Fig.  153.  After  adhesion  of  the  transverse  mesocolon 
continuity  would  be  estabhshed  between  its  upper  or  cephalic 
layer  and  the  secondary  parietal  peritoneum  investing  the  supra- 
colic  portion  of  the  descending  duodenum  (Fig.  154)  while  its 
caudal  layer  becomes  continuous  with  the  secondary  parietal 
peritoneum  covering  the  infra-colic  segment  of  the  duodenum  and 
the  lower  portion  of  the  ventral  surface  of  the  right  kidney. 

Reference  to  the  schematic  Figs.  152,  153  and  154,  will 
show  that  the  adult  duodenum  becomes  fixed  to  the  posterior 
parietes  of  the  abdomen  by  adhesion  of  its  visceral  serous 
covering  and  of  the  dorsal  layer  of  the  mesoduodenum  to 
the  primitive  parietal  peritoneum.  The  supra-colic  segment  of 
the  adult  descending  duodenum  lies  under  cover  of  a  single 
peritoneal  layer,  derived  from  its  own  visceral  investment  and 
appearing  as  secondary  parietal  peritoneum  by  continuity  laterad 
along  the  line  of  adhesion  with  the  primitive  parietal  peritoneum 
covering  the  upper  part  of  ventral  surface  of  right  kidney,  while 
mesad,  the  layer  covering  this  segment  of  the  duodenum,  is  con- 
tinued into  the  secondary  parietal  peritoneum  derived  from  the 
left  or  ventral  leaf  of  the  mesoduodenum  and  covering  the  ven- 
tral surface  of  the  pancreas  (cf  Figs.  138-140). 

On  the  other  hand,  the  infra-colic  segment  of  the  descending 
duodenum,  as  well  as  the  lower  and  mesal  angle  of  the  ventral 
surface  of  right  kidney,  between  ascending  and  transverse  colon, 
is  covered  by  a  layer  of  secondary  parietal  peritoneum  derived 
from  the  ventral  layer  of  the  ascending  mesocolon  and  continu- 
ous with  the  caudal  layer  of  the  transverse  mesocolon.  Beneath 
this  secondary  parietal  peritoneum  are  two  obliterated  layers,  on 
the  one  hand  the  dorsal  layer  of  the  mesocolon,  on  the  other  the 
visceral  infra-colic  duodenal  serosa  and  the  primitive  prerenal 
parietal  peritoneum. 

In  the  further  development  of  the  adult  human  arrangement 
the  changes  below  the  level  of  the  transverse  colon  and  meso- 
colon result  in  the  fixation  of  the  ascending  and  descending  colon 

6 


82  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

to  the  background  of  the  right  and  left  lumbar  regions.  The 
opposed  serous  surfaces  of  the  ascending  and  descending  mesocola 
and  of  the  dorsal  parietal  peritoneum  adhere  and  the  process  also 
usually  involves  the  dorsal  visceral  peritoneum  of  the  ascending 
and  descending  colon,  so  that  these  portions  of  the  gut  obtain  a 
fixed  position. 

Adhesion  of  the  mesocolon  to  the  dorsal  body  wall  (parietal 
peritoneum)  does  not  occur  at  all  points  at  the  same  time.  Usually 
adhesion  proceeds  from  the  midline  laterad.  The  fixation  of  the 
ascending  colon  in  the  human  embryo  begins  about  the  fourth 
month. 

In  the  descending  segment  by  the  same  time  adhesion  has 
usually  proceeded  nearly  up  to  the  descending  colon,  but  the  in- 
testine itself  is  as  yet  free.  In  the  fifth  month  the  descending 
colon  has  usually  become  fixed  between  the  splenic  flexure  and 
the  beginning  of  the  sigmoidea.  In  the  latter  region  a  free  meso- 
colon usually  persists  throughout  life. 

Differences  in  the  rate  of  growth  between  the  length  of  the 
body  wall  and  the  length  of  the  mesocolon  may  play  an  impor- 
tant part  in  the  production  of  peritoneal  fossas,  small  pouches 
which  in  some  regions  of  the  abdomen  may  assume  considerable 
proportions.  Such  fossae  are  found  around  the  duodeno-jejuneal 
angle,  the  caecum  and  appendix,  and  the  sigmoid  flexure.  They 
will  be  considered  more  in  detail  with  these  respective  regions, 
especially  in  reference  to  their  relation  to  retro-peritoneal  hernia. 

In  a  certain  proportion  of  cases  adhesion  between  the  parietal 
peritoneum  and  the  ascending  and  descending  mesocolon  is  incom- 
plete or  entirely  wanting,  resulting  in  the  formation  of  a  more  or 
less  completely  free  ascending  and  descending  mesocolon.  Treves, 
in  an  examination  of  100  bodies,  obtained  the  following  figures : 

In  52  subjects  there  was  neither  an  ascending  nor  a  descending 
mesocolon,  the  intestine  being  fixed  in  the  manner  which  is  re- 
garded as  normal. 

In  22  there  was  a  descending,  but  no  trace  of  an  ascending 
mesocolon. 


ASCENDING  AND  DESCENDING  MESOCOLA  IN  ADULT.  83 

In  14  a  mesocolon  was  found  in  both  the  ascending  and  de- 
scending segments  of  the  large  intestine. 

In  12  there  was  an  ascending  mesocolon,  but  no  corresponding 
fold  on  the  left  side.  Hence  from  this  series  a  mesocolon  may 
be  expected  on  the  left  side  in  36  per  cent.,  on  the  right  side  in 
26  per  cent.  ^ 

Both  development  and  comparative  anatomy  would  lead  us  to 
expect  that  the  descending  mesocolon  would  be  found  more  fre- 
quently than  the  ascending. 

In  the  lower  animals  the  descending  mesocolon  is  always  an 
extensive  and  conspicuous  membrane.  It  is  well  developed  in  all 
monkeys  and  the  anthropoidea,  as  the  remains  of  the  primary 
vertical  fold  of  the  dorsal  mesentery,  while  the  ascending  meso- 
colon is  a  secondary  production,  acquired  during  the  development 
of  the  bowel  by  rotation. 

In  most  of  the  lower  monkeys  the  ascending  mesocolon  is  also 
largely  or  entirely  free.  The  descending  mesocolon  can  always 
in  these  animals  be  reflected  to  the  median  line  (cf  Fig.  155). 

The  line  of  attachment  in  man  of  the  descending  mesocolon  is 
usually  along  the  lateral  border  of  the  left  kidney  and  vertical, 
while  the  line  of  attachment  of  the  ascending  mesocolon  is  usually 
less  vertical,  crossing  the  caudal  end  of  the  right  kidney  obliquely 
from  right  to  left  and  with  an  upward  direction  (Fig.  156). 

In  Uke  manner  when  both  the  ascending  and  descending  meso- 
cola  are  absent  as  free  membranes  the  left  or  descending  colon  is 
adherent  along  the  lateral  border  of  the  kidney  to  the  abdominal 
parietes,  while  the  ascending  colon  is  fixed  at  the  hepatic  flexure 
a  little  obliquely  across  the  ventral  surface  of  the  caudal  end  of 
the  corresponding  gland  ascending  toward  the  medial  margin. 

Treves  found  in  the  cases  of  persistent  ascending  mesocolon  in  the 
adult  that  the  membrane  varied  in  breadth  from  1"  to  2"  while  the 
persistent  fold  on  the  left  side  varied  between  2"  and  3"  in  breadth. 

In  the  foetus,  up  to  5"-6"  in  length,  the  descending  mesocolon 
is  usually  an  extensive  fold.  Its  attachment  is  vertical,  but  nearer 
to  the  median  line  than  in  the  adult,  usually  along   the  medial 


84  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

border  of  the  left  kidney.  It  is  at  times  found  attached  along 
this  line  in  the  adult. 

An  ascending  mesocolon  is  rare  even  in  the  foetus.  The  caecum 
and  beginning  of  the  ascending  colon  are  complete^  invested  by 
peritoneum,  but  above  the  parts  so  invested  the  colon  is  usually 
adherent  along  an  oblique  line  to  the  ventral  and  medial  aspect 
of  the  right  kidney. 

In  the  foetus  at  full  term,  if  the  caecum  is  still  undescended  and 
in  contact  with  the  liver,  it  is  not  uncommon  to  find  the  cephalic 
portion  of  the  descending  colon  provided  with  a  mesocolon,  while 
the  caudal  part  of  the  descending  colon  is  fixed  by  adhesion  to 
the  ventral  surface  and  lateral  border  of  the  left  kidney.  This 
free  membrane  is  then  really  a  part  of  the  transverse  mesocolon. 
Where  the  caecum  descends  to  the  iliac  fossa  the  portion  of  the 
foetal  descending  colon  so  invested  is  drawn  over  to  the  right  and 
incorporated  in  the  transverse  colon. 

Treves  in  two  out  of  100  bodies  found  the  caecum  in  the  right 
iliac  region,  but  both  it  and  the  whole  of  the  ascending  colon 
were  entirely  free  from  any  peritoneal  connections  with  the  dorsal 
parietes  of  the  abdomen. 

The  gut  from  the  tip  of  the  caecum  to  the  hepatic  flexure  was 
entirely  invested  by  peritoneum  continuous  with  the  mesentery. 
The  ascending  colon  was  covered  in  the  same  manner  and  by  the 
same  fold  as  the  small  intestine.  The  segment  of  large  intestine 
thus  free  measured  8"  in  both  instances. 

The  mesentery  lacked  the  usual  attachment  to  the  dorsal  ab- 
dominal wall  and  its  root  was  represented  by  the  interval  between 
the  duodenum  and  the  transverse  colon.  The  membrane  had  no 
other  than  its  original  primary  attachment,  and  small  intestine 
and  ascending  colon  formed  together  a  loop  that  practically 
represented  the  condition  of  the  great  primary  intestinal  loop. 
(Compare  p.  73.) 

The  arrangement  presented  in  these  two  subjects  corresponds  to 
that  met  in  many  animals,  such  as  the  cat. 

A  cross  section  of  the  cat's  abdomen  arranged  as  above  would 


POSITION  OF  COLIC  SEGMENTS  IN  ADULT.  85 

show  the  following  disposition  of  the  peritoneum,  corresponding 
to  the  stage  in  the  human  development  preceding  the  fixation  of 
the  two  vertical  colic  segments  (Fig.  157).  It  will  be  seen  that 
the  right  and  left  mesocola  can  be  reflected  to  the  median  line 
where  they  become  continuous  ventrad  of  the  vertebral  column 
and  aorta  with  the  mesentery  of  the  small  intestine.  The  ventral 
surfaces  of  both  kidneys  are  seen  to  be  covered  by  the  primitive 
parietal  peritoneum  of  the  abdominal  cavity. 

Fig.  158  shows  the  adult  human  arrangement  of  the  same  parts, 
after  fixation  of  the  vertical  colic  segments  by  adhesion  of  the 
opposed  surfaces  of  their  mesocola  and  the  primitive  parietal  peri- 
toneum. The  background  of  the  abdomen  is  now  seen  to  be 
covered  by  a  layer  of  secondary  parietal  peritoneum,  viz.,  the 
original  left  leaf  of  the  ascending  and  right  leaf  of  the  descending 
mesocolon,  continuous  above  with  the  lower  or  caudal  layer  of  the 
transverse  mesocolon. 

This  adhesion  is  so  complete  that  the  original  condition  is  dis- 
regarded in  adult  descriptive  anatomy.  The  layer  which  has  ad- 
hered to  the  parietal  peritoneum  can  no  longer  be  recognized  and 
the  other  has  assumed  the  rdle  of  parietal  peritoneum. 

The  connection  of  the  transverse  mesocolon  with  the  dorsal 
lamella  of  the  great  omentum  will  be  considered  below. 

The  course  of  the  vessels  in  the  ascending  and  descending  meso- 
cola is  not  altered  by  the  secondary  adhesions.  These  vessels  are 
in  the  adult  situated  behind  the  secondary  parietal  peritoneum 
derived  from  the  mesocola. 

The  origin  of  the  transverse  mesocolon  obtains  by  the  fixation 
of  the  hepatic  and  splenic  flexures  high  up  in  the  abdomen  a 
transverse  course,  and  the  transverse  growth  of  the  abdomen 
holds  the  membrane  in  this  position  cephalad  of  the  duodeno- 
jejunal flexure,  so  that  on  elevating  the  transverse  colon  the 
mesocolon  appears  as  separating  the  upper  from  the  lower  ab- 
dominal compartment.  This  posterior  line  of  attachment  or  so- 
called  "root  of  the  transverse  mesocolon,"  is  nothing  more  than 
the  upper  limit  of  the  area  of  adhesion  between  the  primitive 


86  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

parietal  peritoneum  and  the  opposed  surfaces  of  the  ascending 
and  descending  mesocola.  Reference  to  the  abdominal  cavity  of 
the  cat  after  complete  rotation  (Fig.  146)  will  show  the  original 
continuity  of  the  three  mesocola  very  clearly.  A  secondary  con- 
nection is  established  along  the  lateral  border  of  ascending  and 
descending  colon  (Fig.  158),  between  the  primitive  parietal  peri- 
toneum and  the  ventral  visceral  peritoneal  investment  of  the 
large  intestine.  Both  of  the  vertical  segments  of  the  colon  now 
appear  fixed.  Their  dorsal  surfaces  are  uncovered  by  peritoneum 
and  can  be  reached  in  the  lumbar  region,  laterad  of  the  kidney, 
without  opening  the  peritoneal  cavity  (lumbar  colotomy). 

The  caudal  portions  of  both  kidneys  are  covered,  beneath  the 
secondary  parietal  peritoneum,  by  a  layer  of  loose  connective  tissue 
representing  the  result  of  obliteration  by  adhesion  of  the  first 
and  second  of  the  original  three  layers  of  prerenal  peritoneum, 
viz.,  the  primitive  parietal  (1)  and  the  two  layers  of  the  mesocola 
(2  and  3). 

Line  of  Attachment  of  the  Mesentery  of  the  Jejuno-ileum. 
— Examination  of  the  caudal  surface  of  the  transverse  mesocolon 
in  the  cat,  with  the  parts  in  the  above  outlined  position,  will  show 
how  and  why  in  the  adult  human  abdomen  the  duodeno-jejunal 
angle  appears  to  dip  out  from  beneath  the  transverse  mesocolon, 
becoming  gradually  more  and  more  free  until  complete  transition 
to  the  mobile  jejunum  is  obtained.  From  this  point,  situated  to 
the  left  of  the  second  lumbar  vertebra,  the  dorsal  attachment 
of  the  adult  human  mesentery  of  the  jejuno-ileum  extends  some- 
what obliquely  caudad  and  to  the  right  to  terminate  in  the  right 
iliac  fossa  at  the  ileo-colic  junction. 

Returning  to  the  conditions  presented  by  the  cat's  intestines 
to  obtain  an  explanation  of  this  line  of  fixation  we  must  recall 
the  fact  that  in  the  peritoneum  included  within  the  limits  of  the 
umbilical  loop,  after  differentiation  of  small  and  large  intestine, 
but  before  rotation,  we  have  both  the  elements  of  the  mesentery 
of  the  small  intestines  and  of  the  ascending  and  transverse  meso- 
colon combined  (Fig.  141).     For  it  will  be  seen  that  this  mem- 


MESENTERY  OF  JEJUNO-ILEUM.  87 

brane  carries  at  this  time  vessels  both  to  the  jejuno-ileum  and  to 
the  segments  of  the  large  intestine  (caecum,  ascending  and  trans- 
verse colon).  This  fact  will  be  at  once  recognized  if  the  cat's  in- 
testines are  arranged  to  correspond  to  the  primitive  condition 
(Fig.  136)  and  the  mesentery  examined. 

After  rotation  and  differentiation  of  the  colic  segments  and  after 
the  adhesion  of  the  ascending  and  descending  colon  in  man,  the 
course  of  the  main  trunk  of  the  superior  mesenteric  artery  passes, 
after  crossing  the  third  portion  of  the  duodenum,  down  and  to  the 
right  to  terminate  near  the  ileo-colic  junction  by  anastomosis  with 
its  ileo-colic  branch.  The  adhesion  of  the  right  and  left  meso- 
cola  to  the  dorsal  parietal  peritoneum  proceeds  mesad  as  far  as 
this  line,  leaving  free  the  mesentery  of  the  small  intestines,  which 
contains  the  vasa  intestini  tenuis  derived  from  the  left  side  of  the 
main  vessel.  The  secondary  line  of  attachment  of  the  mesentery 
to  the  abdominal  background  is  therefore  along  this  line.  To 
obtain  a  clear  idea  of  these  processes  of  development  in  man  as- 
sume that  in  the  cat,  after  rotation  and  establishment  of  the  three 
divisions  of  the  colon,  the  two  vertical  (ascending  and  descending) 
mesocola  become  adherent  to  the  dorsal  parietal  peritoneum,  leav- 
ing the  mesentery  of  the  small  intestine  free. 

Fig.  159  illustrates  schematically  the  area  of  mesocolic  adhe- 
sion in  the  human  subject  after  complete  rotation,  and  the  Hne  of 
the  mesentery  of  jejuno-ileum. 

Fixation  of  the  ascending  and  descending  cola  and  of  their 
mesocola  proceeds  cephalad  as  far  as  the  line  AB,  which  thereby 
constitutes  the  root  of  the  free  transverse  mesocolon. 

The  secondary  parietal  peritoneum  derived  from  the  ventral 
layer  of  the  ascending  mesocolon  covers  the  lower  and  inner  por- 
tion of  the  ventral  surface  of  the  right  kidney,  the  infra-colic 
division  of  the  descending  and  the  dextro-mesenteric  segment  of 
the  transverse  duodenum,  while  along  the  root  of  the  jejuno-ileal 
mesentery  it  becomes  continuous  with  the  right  layer  of  that  mem- 
brane. The  secondary  parietal  peritoneum  derived  from  the  ven- 
tral layer  of  the  descending  colon  covers  the  lower  part  of  the  ven- 


88  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

tral  surface  of  the  left  kidney  and  the  sinistro-mesenteric  segment 
of  the  transverse  duodenum  and  becomes  continuous  along  the 
mesenteric  radix  with  the  left  layer  of  the  jejuno-ileal  mesentery. 

Caudad  the  adhesion  of  the  descending  colon  and  mesocolon  to 
the  parietal  peritoneum  proceeds  only  to  the  point  C,  following 
the  dotted  line  mesad  and  resulting  in  the  formation  of  the  free 
mesocolon  of  the  sigmoid  flexure. 

Resume  of  the  Adult  Arrangement  of  the  Human  Peritoneum  in  the 
Lower  Compartment  of  the  Abdomen,  Below  the  Level  of  the  Trans- 
verse Colon  and  Mesocolon. — ^We  should  now  consider  the  arrange- 
ment of  the  human  peritoneum  in  the  adult  below  the  dorsal 
attachment  of  the  transverse  meso-colon  in  the  light  of  the  em- 
bryological  and  comparative  anatomical  facts  just  stated.  In 
doing  this  it  will  be  advisable  to  study  both  the  actual  conditions 
encountered  and  their  significance  in  the  sense  of  determining 
the  derivation  of  the  peritoneal  layers  from  the  primitive  dorsal 
mesentery.  Open  the  abdominal  cavity  in  the  usual  manner  by 
a  cruciform  incision. 

Turn  the  great  omentum  up  on  the  chest  wall,  exposing  the 
underlying  intestines.  This  manipulation,  as  already  stated,  will 
cause  the  omentum  to  carry  the  transverse  colon  with  it,  on 
account  of  the  adhesion,  in  the  adult,  of  the  gut  to  the  dorsal 
layer  of  the  omentum.  Hence  the  cephalic  or  upper  layer  of  the 
transverse  mesocolon  will  not  be  seen  at  this  stage  because  the 
omental  adhesion  just  referred  to  prevents  us  from  passing  be- 
tween the  greater  curvature  of  the  stomach  and  the  transverse 
colon  without  tearing  peritoneal  layers.  It  will,  however,  be  pos- 
sible to  trace  on  the  right  side  the  duodenum  from  the  pylorus 
down  ventrad  of  the  right  kidney  until  the  descending  portion 
disappears  behind  the  hepatic  flexure  of  the  colon.  With  the 
omentum  and  transverse  mesocolon  turned  up,  as  stated,  and  the 
transverse  mesocolon  put  upon  the  stretch,  it  will  be  seen  that  the 
abdominal  space  now  overlooked  is  bounded  cephalad  by  the 
lower  layer  of  the  transverse  mesocolon  and  its  attachment  to  the 
dorsal  abdominal  wall.     The  lateral  limits  of  the  space  are  given 


ADULT  PERITONEAL  RELATIONS  IN  INFRA-COLIC  COMPARTMENT.  89 

by  the  ascending  and  descending  colon  respectively.  The  attach- 
ment of  the  mesentery  of  the  small  intestine  to  the  oblique  line 
extending  from  the  left  of  the  vertebral  column  at  about  the 
level  of  the  second  lumbar  vertebra  to  the  right  iliac  fossa  sub- 
divides the  entire  space  into  a  secondary  right  and  left  compart- 
ment. 

Begin  by  following  the  caudal  layer  of  the  transverse  meso- 
colon dorsad  on  the  right  side.  In  the  angle  between  ascending 
and  transverse  colon  (hepatic  flexure)  pressure  will  locate  the 
caudal  portion  of  the  ventral  surface  of  the  right  kidney.  Re- 
member that  the  peritoneum  touched  in  these  procedures  appears 
in  the  adult  as  parietal  prerenal  peritoneum,  but  that  in  reality 
it  is  the  left  leaf  of  the  originally  free  ascending  mesocolon,  whereas 
the  original  right  leaf  of  this  membrane  and  the  primitive  parietal 
peritoneum  have,  by  adhesion  of  their  serous  surfaces,  been  con- 
verted into  the  loose  subserous  connective  tissue  covering  the 
ventral  aspect  of  the  kidney  beneath  what  now  appears  as 
parietal  peritoneum. 

Mesad  of  the  resistance  offered  to  the  finger  by  the  right  kidney 
the  caudal  (infra-colic)  portion  of  the  descending  duodenum  and 
the  angle  of  transition  between  it  and  the  third  or  transverse 
portion  will  be  found,  invested  in  the  same  way  by  secondary 
(mesocolic)  parietal  peritoneum.  It  will  be  seen,  especially  if  the 
duodenum  is  injected  or  inflated,  that  the  hepatic  flexure  of  the 
colon  lies  ventrad  of  the  vertical  descending  second  portion  of  the 
duodenum,  so  that  one  part  of  this  intestine  is  situated  cephalad 
the  other  caudad  of  the  colon.  (Supra-  and  infra-colic  segments 
of  descending  duodenum.) 

Individual  differences  are  observed  in  the  area  of  colic  attach- 
ment to  the  duodenum.  Usually  the  two  intestines  are  in  con- 
tact with  each  other  and  adherent  over  a  considerable  surface. 
Exceptionally  the  transverse  mesocolon  extends  across  to  the 
right  so  as  to  include  the  hepatic  flexure. .  In  this  latter  case  the 
uncovered  non-peritoneal  surface  of  the  descending  duodenum  is 
small,  represented  by  the  interval  between  the  layers  of  the  trans- 


90  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

verse  mesocolon,  and  the  hepatic  flexure  is  then  not  directly  ad- 
herent to  the  gut. 

If  we  now  trace  the  transverse  duodenum  from  right  to  left  w^ 
will  encounter  the  right  layer  of  the  root  of  the  jejuno-ileal  mes- 
entery. The  caudal  layer  of  the  transverse  mesocolon,  the  right 
leaf  of  the  mesentery  and  the  secondary  parietal  peritoneum  invest- 
ing the  ventral  surface  of  the  transverse  duodenum  all  meet  at 
this  point.  Surround  the  mesentery  of  the  free  small  intestine 
with  the  fingers  of  one  hand  so  that  the  entire  mass  of  intestinal 
coils  can  be  swung  alternately  from  side  to  side. 

Turning  them  over  to  the  left,  as  already  stated,  the  proximal 
portion  of  the  transverse  duodenum  can  be  traced  from  right  to 
left  as  far  as  the  root  of  the  mesentery.  Here  the  peritoneum 
investing  the  ventral  surface  of  the  duodenum  becomes  con- 
tinuous with  the  right  leaf  of  the  mesentery.  Now  swing  the 
whole  mass  of  small  intestines  over  to  the  right,  exposing  the 
parietal  peritoneum  in  the  space  to  the  left  of  the  vertebral 
column,  between  the  attachment  of  the  mesentery  to  the  median 
side,  the  root  of  transverse  mesocolon  cephalad  and  the  descend- 
ing colon  to  the  left.  Remember  that  the  same  significance  at- 
taches to  this  secondary  parietal  peritoneum  as  on  the  right  side. 
It  appears  in  the  adult  as  parietal  peritoneum,  but  is  in  its  deri- 
vation the  original  right  leaf  of  the  descending  mesocolon.  Close 
to  the  root  of  the  mesentery  the  continuation  from  the  right  side 
of  the  transverse  duodenum  will  be  seen,  crossing  the  median  line 
from  right  to  left  ventrad  of  aorta  and  vertebral  column  and  usu- 
ally turning  cephalad  on  the  left  side  of  the  lumbar  vertebrae,  as 
the  fourth  or  ascending  duodenum,  to  reach  the  caudal  surface  of 
the  transverse  mesocolon  near  its  attachment,  where  the  gut  turns 
ventrad  to  form  the  duodeno-jejunal  angle  and  become  continuous 
with  the  free  small  intestine. 

From  the  fact  that  the  transverse  duodenum  is  thus  seen  on 
each  side  of  the  root  of  the  mesentery  it  will  be  recalled  that 
after  rotation  of  the  primitive  intestine  the  superior  mesenteric 
artery  crosses  the  transverse  portion  of  the  duodenum  to  reach  its 


ADULT  PERITONEAL  RELATIONS  IN  INFRA-COLIC  COMPARTMENT.    91 

distribution  between  the  leaves  of  the  mesentery.  Hence  this 
portion  of  the  small  intestine  consists  of  a  dextro-  and  sinistro- 
mesenteric  segment.  This  intersection  of  mesentery  and  duode- 
num marks  the  site  of  the  primitive  duodeno-colic  -isthmus 
through  which  the  superior  mesenteric  artery  passed  to  reach  its 
distribution  to  the  gut  composing  the  embryonic  umbilical  loop. 

To  the  left  of  the  ascending  duodenum  a  portion  of  the  caudal 
surface  of  the  pancreas  will  be  seen,  covered  by  the  continuation 
of  the  caudal  leaf  of  the  transverse  meso-colon  into  the  parietal 
peritoneum.  The  consideration  of  this  relation  of  peritoneum 
and  pancreas  will  profitably  be  deferred  until  we  have  studied 
the  developmental  changes  in  the  region  of  the  dorsal  meso- 
gastrium  and  great  omentum. 

In  the  angle  between  termination  of  the  transverse  colon  and 
proximal  part  of  descending  colon  (splenic  flexure)  the  caudal 
part  of  the  ventral  surface  of  the  left  kidney  will  be  felt.  The 
disposition  of  the  peritoneum  and  its  significance  is  the  same  as  on 
the  right  side.  Inasmuch  as  we  have  already  seen  that  the  sec- 
ondary parietal  peritoneum  covering  the  dorsal  abdominal  wall 
on  each  side  of  the  small  intestine's  mesenteric  attachment  is  de- 
rived from  the  primitive  ascending  and  descending  mesocolon,  it 
will  be  readily  understood  why  the  blood  vessels  supplying  the 
ascending  and  descending  colon  (arteria  ileo-colica,  a.  colica  dextra, 
a.  colica  sinistra)  are  placed  beJmid  the  parietal  peritoneum,  while 
the  colica  media,  supplying  the  transverse  colon,  runs  between  the 
layers  of  the  transverse  mesocolon.  Originally  the  same  condition 
obtained  for  the  two  vertical  colic  segments,  but  with  the  anchor- 
ing of  these  portions  of  the  large  intestine  and  the  adhesion  of  their 
mesocola  to  the  parietal  peritoneum  the  blood  vessels  which  for- 
merly ran  between  the  two  layers  of  the  membrane,  as  long  as  it  re- 
mained free,  now  appear  as  retroperitoneal  vessels  placed  beneath 
the  parietal  peritoneum  derived  secondarily  from  the  mesocola. 

This  fact  must  be  borne  in  mind  in  studying  the  arrangement 
of  certain  folds  and  fossae  of  the  parietal  peritoneum  which  are 
now  to  be  considered. 


92  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

Duodenal  Fossae.   Fossa  of  Treitz  and  Retro-peritoneal  Hernia The 

peritoneal  cavity  of  the  cat  can  be  used  to  great  advantage  in 
order  to  obtain  a  clear  idea  of  the  formation  of  these  folds  and 
fossae,  whose  relation  to  the  so-called  "  retro-peritoneal  hernia  " 
has  led  to  an  exaggerated  elaboration  of  minute  detail  and  a 
somewhat  puzzling  terminology  in  human  descriptive  anatomy. 

Directions  for  Examining  the  Folds  and  the  Formation  of  the  Duo- 
deno-jejunal  Fossa  in  the  Cat — ^Turn  the  omentum  and  the  coils  of 
the  small  intestine  cephalad  out  of  the  abdomen  until  they  rest 
upon  the  ventral  thoracic  wall.  Press  the  large  intestine  over  to 
the  left  side,  putting  the  mesocolon  on  the  stretch  until  the  parts 
are  arranged  as  shown  in  Fig.  160.  The  loop  of  the  duodenum 
with  the  head  portion  of  the  pancreas  will  be  seen  caudad  of  the 
liver  and  ventrad  of  the  right  kidney.  A  well-marked  peritoneal 
fold,  somewhat  sickle-shaped,  with  the  concavity  of  the  free  edge 
directed  caudad  and  to  the  right,  will  be  seen  extending  from  the 
convex  border  of  the  duodenum,  directly  opposite  the  mesenteric 
or  attached  margin,  to  the  right  leaf  of  the  mesocolon.  This 
fold  indicates  the  beginning  adhesion  of  the  duodenum  to  the 
mesocolic  peritoneum,  the  first  step  toward  the  subsequent  com- 
plete fixation  of  the  gut  as  it  is  found  in  man. 

Fig.  161  shows  the  abdominal  cavity  of  Nasua  rufa,  the  brown 
Coati-mundi,  a  South  American  arctoid  carnivore,  with  the  in- 
testines everted  and  turned  to  the  left  side.  In  this  animal  the 
large  intestine  is  very  short,  there  is  no  caecum,  the  ileo-colic 
junction  is  only  marked  on  the  surface  by  a  pyloric-like  constric- 
tion of  the  tube  and  in  the  interior  by  the  projection  of  a  ring- 
valve  (Fig.  408). 

The  duodenal  fold  is  very  well  developed,  passing  between  the 
convex  surface  of  the  duodenal  loop  and  the  adjacent  right  leaf  of 
the  short  mesocolon. 

In  Primates,  in  which  complete  rotation  of  the  intestine,  on 
the  plan  of  the  human  development,  takes  place,  still  further  and 
more  extensive  agglutination  of  the  serous  surface  of  the  duode- 
num to  the  peritoneum  of  the  mesocolon  occurs.     Fig.  162  shows 


DUODENO-JEJUNAL  FOLD  AND  FOSSA   IN  THE  CAT.  93 

the  condition  in  Hapale  vulgaris,  one  of  the  marmosets.  The  as- 
cending and  descending  mesocola  and  the  mesoduodenum  of  this 
animal  are  still  free,  but  the  surface  of  the  duodenum  has  become 
fastened  to  the  opposed  mesocolon.  With  fixation  of  the  hepatic 
flexure  and  adhesion  of  the  ascending  colon,  such  as  occurs  in 
man,  the  duodenum  is  carried  dorsad  against  the  ventral  surface 
of  the  right  kidney,  and  now  anchoring  of  the  duodenum,  by  ob- 
literation of  the  mesoduodenum  and  adhesion  to  the  prerenal 
parietal  peritoneum,  takes  place  as  already  detailed  above.  To 
return  now  to  the  formation  of  the  duodeno-jejunal  fossa  by 
means  of  this  fold,  as  illustrated  in  the  cat.  Perform  the  manipu- 
lations already  described  in  rotation  of  the  intestine.  The  appear- 
ance of  the  parts  then  will  be  as  shown  in  Fig.  163.  The  large 
intestine  is  drawn  over  so  as  to  represent  the  human  ascending 
and  transverse  colon  in  one  segment,  the  descending  colon  in  the 
other,  and  the  mesocolon  appears  correspondingly  as  transverse 
and  descending.  In  other  words  the  cat's  intestines  as  arranged 
in  the  figure  would  represent  the  stage  in  the  human  develop- 
ment in  which  caecum  and  beginning  of  large  intestine  are  still 
subhepatic  in  position  ventrad  of  the  right  kidney,  before  differen- 
tiation of  ascending  and  transverse  colon  by  descent  of  caecum 
into  right  iliac  fossa. 

In  the  human  subject,  as  we  have  seen,  the  transverse  meso- 
colon obtains  a  secondary  attachment  to  the  background  of  the 
abdominal  cavity,  its  caudal  surface  remaining  free. 

The  descending  mecocolon  turns  its  original  right  leaf  ventrad, 
its  left  leaf  dorsad,  and  the  latter  adheres  to  the  primitive  parietal 
peritoneum  covering  the  left  lumbar  region  and  ventral  surface  of 
left  kidney.  This  area  of  adhesion  extends  up  to  and  usually 
involves  the  dorsal  surface  of  the  descending  colon,  anchoring 
the  same  in  the  left  lumbar  region,  down  to  the  point  where  the 
sigmoid  flexure  begins  and  where  the  original  mesocolon  again 
appears  free. 

In  the  cat,  therefore,  with  the  intestines  arranged  to  correspond 
to  the  course  of  the  human  large  intestine  after  rotation  has  been 


94  ANATOMY   OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

accomplished,  the  Unas  representing  the  peritoneal  human  adhe- 
sions should  be  fixed,  as  shown  in  the  schema,  Fig.  159  :  ab,  Une 
of  secondary  attachment  after  rotation  resulting  in  the  formation 
of  the  "  root "  of  a  free  transverse  mesocolon,  bc,  line  of  limit  of 
secondary  adhesion  to  the  original  parietal  peritoneum  involving 
the  entire  left  (now  dorsal)  layer  of  the  descending  mesocolon  and 
the  dorsal  surface  of  the  descending  colon,  resulting  in  the  fixa- 
tion of  the  latter  part  of  the  large  intestine. 

This  establishes,  as  already  stated,  a  secondary  parietal  peri- 
toneal surface  in  the  left  lumbar  region  derived  from  the  original 
right  leaf  of  the  descending  mesocolon.  Inasmuch  as  the  infe- 
rior mesenteric  vessels  originally  passed  to  the  descending  colon 
between  the  layers  of  the  mesocolon  they  will  now  apparently  be 
placed  beneath  the  (secondary)  parietal  peritoneum  of  the  left 
lumbar  region. 

If  now  the  duodenal  fold  in  the  cat  be  examined  after  rotation 
of  the  intestine  it  will  be  found  presenting  the  original  relations 
(Figs.  160  and  163),  viz.,  passing  from  the  convex  margin  of  that 
portion  of  the  duodenal  loop  which  would  correspond  to  the  human 
fourth  or  ascending  portion,  to  the  original  right  layer  of  the  meso- 
colon, which  in  man  becomes  secondarily  converted  into  the 
parietal  peritoneum  of  the  left  lumbar  region.  Hence  the  connec- 
tions of  the  fold  are  as  follows  : 

On  the  right :  ventral  surface  of  the  ascending  duodenum. 

On  the  left :  right  layer  of  mesocolon  (secondary  lumbar  parietal 
peritoneum  in  the  adult  human  subject). 

Cephalad  it  abuts  against  the  caudal  layer  of  the  transverse  meso- 
colon along  the  line  which  would  correspond  to  the  root  of  the 
mesocolon  in  the  adult  human  subject. 

The  concave  caudal  edge  is  free  and  bounds  the  entrance  into  a 
fossa,  the  "superior  duodenal  fossa"  of  anthropotomy.  This  fossa 
opens  caudad  and  extends  cephalad  to  the  root  of  the  transverse 
mesocolon.  The  ventral  and  left  wall  of  the  fossa  is  formed  by 
the  fold  in  question,  its  background  by  the  mesocolon  (right 
leaf) ;  to  the  right  the  left  circumference  of  the  ascending  duo- 


DUODENO-JEJUNAL  FOLDS  AND  FOSSM  IN  MAN.  95 

denum  enters  into  the  formation  of  the  fossa,  and  its  fundus  is 
formed  by  the  confluence  of  the  fold  and  of  the  caudal  layer  of 
the  transverse  mesocolon.  The  inferior  mesenteric  vessels  are 
found  near  the  left  margin  of  the  entrance  into  the  fossa. 

Fig.  164  shows  the  appearance  of  the  fold  in  Nasua  rufa  after 
rotation  of  the  intestine.  The  short  course  of  the  large  intestine  in 
this  animal,  and  the  consequent  reduction  of  the  mesocolon,  brings 
the  fold  much  below  the  level  which  it  occupies  in  the  cat. 

If  we  now  look  for  the  corresponding  structures  in  man  we  will 
find  certain  modifications  depending  chiefly  upon  still  closer  ad- 
hesion between  duodenum  and  the  mesocolon  which  is  destined 
to  become  the  left  parietal  peritoneum  after  anchoring  of  the 
descending  colon.  We  have  already  encountered  an  example  of 
such  closer  connection  in  the  marmoset  shown  in  Fig.  162. 

In  all  cases  the  "superior  duodenal"  fold,  corresponding  to  the 
fold  just  encountered  in  the  cat,  is  the  original  condition,  and  the 
duodenal  fossa  consequently  opens  caudad.  In  many  instances 
this  will  be  the  only  fold  and  fossa  encountered  in  the  adult 
human  subject.  In  other  instances  more  extensive  duodeno-meso- 
colic  adhesions  result  in  the  addition  of  an  "inferior  fold," 
bounding  a  fossa  the  entrance  into  which  is  directed  cephalad  to- 
ward the  transverse  mesocolon.  Such  a  condition  is  seen  in  Fig. 
165  taken  from  a  foetus  at  term.  The  duodenal  fossa  in  this  case 
is  bounded  by  an  "  upper  "  and  "lower  "  duodenal  fold  continuous 
with  each  other  on  the  left  side,  but  separated  on  the  right  at  their 
attachment  to  the  duodenum.  It  will  be  seen  that  the  inferior 
mesenteric  vein  runs  in  the  left  margin  of  the  fold,  following 
along  the  left  border  of  the  entrance  into  the  fossa.  A  segment 
of  the  colica  sinistra  artery  may  occupy  the  same  position.  This 
position  of  the  vein,  or  artery,  or  of  both  vessels,  is  not  the  cause 
leading  to  the  formation  of  the  duodenal  fossa,  but  is  more  or  less 
accidental  and  variable.  In  many  cases  the  vessels  run  at  some 
distance  from  the  folds  bounding  the  fossa. 

In  some  subjects  the  "inferior"  fold  is  the  only  one  found, 
and  the  only  duodenal  fossa  then  encountered  looks  cephalad. 


96  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL  CAVITY. 

This  condition,  when  associated  with  the  course  of  the  inferior 
mesenteric  vessels  in  the  free  edge  of  the  fold,  constituted  the 
classical  "fossa  duodeno-jejunalis"  of  Treitz,  and  is  described  as 
"Treitz's  fossa." 

Fig.  166  shows  the  condition  in  which  only  a  small  inferior  fold 
attaches  itself  to  the  termination  of  the  transverse  duodenum. 
There  is  practically  an  entire  absence  of  duodenal  or  duodeno- 
jejunal folds  and  fossse.  The  inferior  mesenteric  vessels  course 
under  cover  of  the  mesocolic  secondary  parietal  peritoneum,  but 
do  not  produce  a  fold. 

Fig.  167,  from  an  adult  human  subject,  illustrates  the  further 
development  of  the  fossa  from  the  foetal  conditions  shown  in  Fig. 
165.  The  well-marked  duodenal  fossa  is  bounded  by  a  superior 
and  inferior  duodenal  fold,  uniting  laterally  in  a  crescentic  mar- 
gin containing  a  segment  of  the  inferior  mesenteric  vein  and 
colica  sinistra  artery.  The  lower  division  of  the  peritoneal  recess 
thus  produced  corresponds  to  the  typical  (vascular)  "fossa  of 
Treitz."  Mesally  the  projection  of  the  fourth  portion  of  the  duo- 
denum bounds  the  fossa. 

In  Fig.  168,  also  taken  from  an  adult  human  subject,  an  exten- 
sive duodenal  recess  is  bounded  in  the  same  way  by  a  superior 
and  inferior  duodenal  fold.  In  the  interior  of  the  fossa  a  third 
duodenal  reduplication  of  the  peritoneum  ("intermediate  duodenal 
fold")  is  seen,  as  is  also  the  trunk  of  the  inferior  mesenteric  vein, 
while  the  main  trunk  of  the  colica  sinistra  artery  courses  laterally 
behind  the  secondary  mesocolic  parietal  peritoneum  near  the 
margin  of  the  descending  colon. 

It  will  be  seen  that  the  freedom  of  the  ascending  or  fourth  por- 
tion of  the  duodenum  depends  largely  upon  the  disposition  and 
extent  of  these  folds.  Inasmuch  as  they  are  the  product  of  vary- 
ing degrees  of  adhesion  of  this  segment  of  the  intestine  they  are 
subject  to  great  individual  variations  and  have  given  rise  to  an 
unnecessary  and  complicated  classification  of  the  duodenal  folds 
arid  fossae.  The  close  relation  maintained  between  the  duodeno- 
jejunal angle  and  the  caudal  layer  of  the  transverse  mesocolon 


FOSSA  INTERSIQMOIDEA.  97 

near  its  root  at  times  leads  to  the  production  of  a  peritoneal  fold 
connecting  this  membrane  with  the  duodeno-jejunal  knuckle  of 
intestine  (duodeno-jejunal  or  mesocolic  fold)  and  may  result  in 
the  formation  of  a  duodeno-jejunal  or  mesocolic  fossa  of  the  peri- 
toneum.    An  instance  of  this  fold  is  seen  in  Fig.  168. 

The  importance  of  the  duodenal  fossae,  and  of  similar  peritoneal 
recesses  in  other  parts  of  the  abdominal  cavity,  is  founded  on  the 
fact  that  by  gradual  enlargement  they  may  lodge  the  greater  part 
of  the  movable  small  intestine  in  their  interior,  leading  to  the 
formation  of  intra-  or  retro-peritoneal  hernise.^ 

Fossa  Intersigmoidea. — A  second  peritoneal  pocket  or  fossa  is 
encountered  in  the  region  of  the  sigmoid  flexure  and  its  meso- 
colon. The  formation  of  this  fossa  is  closely  associated  with  the 
adult  disposition  of  the  sigmoid  mesocolon  as  part  of  the  original 
primitive  vertical  dorsal  mesentery.  In  the  typical  arrangement 
of  the  parts  the  sigmoid  or  omega  loop  of  the  large  intestine  has 
a  free  mesocolon.  The  adhesion  of  the  descending  mesocolon  to 
the  parietal  peritoneum  usually  ceases  along  a  line  drawn  hori- 
zontally from  the  lateral  margin  of  the  left  psoas  at  a  level  with 
the  crest  of  the  ilium  to  the  medial  side  of  the  iliac  vessels.  This 
line,  along  which  the  mesocolon  ceases  to  be  adherent  to  the  pa- 
rietal peritoneum,  joins  the  attachment  of  the  distal  portion  of 
the  sigmoid  mesocolon,  which  partially  retains  its  primitive  ver- 
tical origin  to  the  dorsal  midline,  at  a  right  angle.  This  angle 
is  the  site  of  the  intersigmoid  fossa,  the  entrance  into  which  is 
seen  usually  as  a  round  opening  of  variable  size  on  elevating  the 
sigmoid  flexure  and  putting  its  mesocolon  on  the  stretch.  Fig. 
159  shows  the  area  of  adhesion  between  the  primitive  descending 
mesocolon  and  the  parietal  peritoneum  (from  c  mesad)  which  re- 
sults in  the  formation  of  a  free  mesocolon  for  the  sigmoid  flexure. 
Frequently  in  the  angle  formed  by  the  horizontal  and  vertical 
line  of  attachment  of  the  sigmoid  mesocolon  a  non-adherent 
strip  of  the  primitive  mesocolon  roofs  in  a  more  or  less  extensive 

^  For  fnll  details  of  the  anatomical  and  i>atbological  conditions  involved  consult  B.  G. 
A.  Moynihan  "On  Retro-peritoneal  Hernia" — London,  1899. 

7 


98  ANATOMY  OF  PERITONEUM  AND  ABDOMINAL   CAVITY. 

intersigmoid  fossa,  whose   fundus  is   directed  upwards  and  in- 
wards. 

Caecum,  Appendix  and  Ileo-colic  Junction. — Several  peritoneal 
fossae  and  folds  are  found  in  the  ileo-colic  region  in  connection 
with  the  csecum,  appendix  and  termination  of  the  ileum.  The 
practical  importance  of  this  portion  of  the  intestinal  tract  and 
the  great  morphological  interest  which  attaches  to  the  same  make 
it  worth  while  to  consider  its  anatomy  in  a  separate  chapter. 


PART  II. 

ANATOMY  OF  THE  PERITONEUM  IN  THE 

SUPRA-COLIC  COMPARTMENT  OF 

THE  ABDOMEN. 

We  have  already  seen  that  the  transverse  colon  and  meso- 
colon effect  a  general  division  of  the  adult  human  abdominal 
cavity  into  a  cephalic  supra-colic  compartment,  situated  between 
the  diaphragm  and  the  level  of  the  transverse  colon  and  meso- 
colon, comprising  in  general  the  hypochondriac  and  epigastric 
regions,  and  a  larger  caudal  infra-colic  space  which  includes  the 
entire  rest  of  the  abdominal  cavity  and  is  continued  caudad  into  the 
pelvic  cavity.  The  arrangement  of  the  peritoneum  and  viscera 
in  this  latter  space  has  just  been  considered.  The  fact  will  be 
recalled  that  the  second  or  descending  portion  of  the  duodenum, 
passing  dorsad  of  the  hepatic  colic  flexure,  forms  so  to  speak  the 
visceral  connection  between  the  portions  of  the  alimentary  tube 
situated  in  the  supra-colic  compartment  and  those  situated  in  the 
infra-colic  space.  The  fixation  of  this  segment  of  the  duodenum 
and  its  consequent  secondary  retroperitoneal  position  in  the  adult 
human  subject  masks  this  continuity  of  the  alimentary  canal  to 
a  certain  extent  so  that  it  requires  more  than  a  superficial  exami- 
nation in  order  to  trace  correctly  the  course  of  the  duodenum 
from  the  pylorus  to  the  duodeno-jejunal  angle,  dorsad  of  the 
colon,  root  of  transverse  mesocolon  and  mesentery,  and  under 
cover  of  the  secondary  parietal  peritoneum. 

We  have  now  to  turn  our  attention  to  the  viscera  contained  in 
the  cephalic  or  supra-colic  compartment  of  the  abdomen  and  to 
consider  the  disposition  of  the  serous  membrane  investing  them 
and  connecting  them  with  each  other  and  with  the  abdominal 
parietes. 

The  visceral  contents  of  the  supra-colic  compartment  comprise 

99 


100  ANATOMY  OF  THE  PERITONEUM. 

the  liver,  pancreas,  spleen,  stomach  and  the  proximal  portion  of 
the  duodenum,  including  the  hepatic  angle  and  the  supra-colic 
part  of  the  descending  duodenum.  Less  directly  the  cephalic 
portions  of  the  right  and  left  kidney  and  the  corresponding  supra- 
renal capsules  belong  to  this  visceral  group. 

In  this  region  of  the  abdomen  we  meet  with  the  most  exten- 
sive modifications  of  the  primitive  dorsal  peritoneal  membrane, 
producing  conditions  which,  considered  without  reference  to  devel- 
opment and  comparative  anatomy,  are  complex  and  difficult  of 
comprehension.  These  changes  lead  to  the  formation  of  the  so- 
called  "  lesser  sac,"  a  term  which  in  some  respects  is  unfortunate 
as  it  implies  a  more  complete  degree  of  separation  from  the  gen- 
eral peritoneal  cavity  or  "  greater  sac  "  than  actually  exists. 

In  order  to  clearly  understand  the  adult  arrangement  of  the 
peritoneum  in  this  region  it  is  advisable  to  consider  the  subject 
in  two  distinct  subdivisions,  dealing  successively  with  the  two 
cardinal  facts  which  contribute  to  effect  the  change  from  the  sim- 
ple primitive  to  the  complicated  adult  condition. 

These  two  main  elements  are : 

1.  Developmental  changes  in  the  position  of  the  stomach,  al- 
terations in  the  disposition  of  the  proximal  part  of  the  primitive 
dorsal  mesentery  attached  to  the  stomach,  and  the  development 
of  pancreas  and  spleen  in  connection  with  this  membrane. 

2.  The  development  of  the  liver  and  the  successive  stages  in 
the  production  of  the  final  adult  vascular  and  serous  relations  of 
this  organ. 

1.  Stomach  and  Dorsal  Mesogastrium. — We  have  already  consid- 
ered the  early  stages  in  the  differentiation  of  the  stomach  from 
the  primitive  intestinal  tube  of  uniform  caliber  (p.  40).  It  will 
be  recalled  that  the  stomach  at  a  certain  period,  while  it  already 
presents  the  main  structural  features  familiar  in  the  adult  organ, 
occupies  a  vertical  position  in  the  abdominal  cavity,  turning  its 
concave  margin  (lesser  curvature)  ventrad,  while  the  convex  dor- 
sal border  (greater  curvature)  is  directed  toward  the  vertebral 
column,  being  attached  to  the  same  by  the  layers  of  the  proximal 


STOMACH  AND  DORSAL  MESOGASTRIUM.  101 

part  of  the  primitive  dorsal  mesentery.  At  this  time  the  stomach 
presents  right  and  left  surfaces,  and  the  oesophageal  entrance  is 
at  the  highest  or  cephalic  point  of  the  organ,  while  the  pyloric 
transition  to  the  small  intestine  occupies  the  distal  caudal  ex- 
tremity. ~^  " 

The  primitive  dorsal  mesentery,  as  already  stated,  passes  as  a 
thin  double-layered  membrane  between  the  ventral  surface  of  the 
vertebral  column  and  the  dorsal  border  of  the  stomach,  which,  as 
we  will  presently  see,  becomes  during  the  later  stages  of  develop- 
ment the  caudal  (lower)  margin  or  greater  curvature. 

It  will  be  seen  that  the  embryonic  differentiation  of  the  intes- 
tinal tract  into  successive  segments  justifies  the  application  of  a 
terminology  based  on  this  differentiation  to  the  corresponding 
portions  of  the  primitive  common  dorsal  mesentery. 

Thus  the  proximal  portion  extending  between  the  vertebral 
column  and  the  dorsal  border  or  greater  curvature  of  the  stom- 
ach becomes  the  mesogastrium ;  we  differentiate  this  portion 
still  further  as  the  "dorsal  mesogastrium"  to  distinguish  it 
from  a  "ventral  mesogastrium"  which  we  will  presently  encoun- 
ter in  considering  the  development  of  the  liver  and  the  con- 
nected peritoneum. 

In  the  same  way  the  section  of  the  primitive  common  dorsal 
mesentery  attached  to  the  duodenal  loop  becomes  the  mesoduo- 
denum,  that  connected  with  the  mobile  part  of  the  small  intestine 
(jejuno-ileum)  the  mesentery  proper,  while  the  portion  passing  to 
the  colon  forms  the  mesocolon,  to  be  subsequently  still  further 
subdivided,  after  the  different  segments  of  the  large  intestine  have 
become  mapped  out,  as  the  ascending,  transverse  and  descending 
mesocolon,  the  mesosigmoidea  and  the  mesorectum. 

In  tracing  the  development  of  the  adult  human  peritoneum  it 
is  well  to  consider  certain  stages,  which  we  will  find  illustrated  by 
the  permanent  conditions  presented  by  some  of  the  lower  ver- 
tebrates : 
These  stages  comprise : 

(a)  Changes  in  the  position  of  the  stomach. 


102  ANATOMY   OF  THE  PERITONEUM. 

(6)  Changes  in  the  direction  and  extent  of  the  dorsal  meso- 
gastrium. 

(c)  Development  of  the  pancreas  and  spleen  in  connection  with 
the  mesogastrium. 

A.  Changes  in  the  Position  of  the  Stomach. 

The  primitive  position  of  the  organ  above  outlined  (p.  41)  is 
changed  during  the  course  of  further  development  by  a  twofold 
rotation. 

1.  The  primitive  vertical  position,  in  which  the  oesophageal  en- 
trance occupies  the  highest  cephalic  extremity,  while  the  pyloric 
opening  is  at  the  opposite  caudal  end,  is  exchanged  for  one  directed 
more  transversely,  approximating  the  two  gastric  orifices  to  the 
same  horizontal  level.  In  human  embryos  of  13.9  mm.  the  fundus 
has  already  descended,  the  pylorus  moving  cephalad  and  to  the 
right,  while  the  cardia  becomes  shifted  more  to  the  left.  At  the 
same  time  the  greater  growth  and  prominence  of  the  convex  border 
or  greater  curvature  becomes  marked  in  comparison  with  the  rela- 
tively short  extent  of  the  opposite  margin  or  lesser  curvature. 

2.  Coincident  with  this  change  in  position  is  a  rotation  around 
the  vertical  axis,  by  means  of  which  the  original  left  side  of  the 
stomach  is  turned  ventrad,  becoming  the  ventral  or  "  anterior  " 
surface,  while  the  original  right  surface  of  the  organ  now  looks 
dorsad  toward  the  vertebral  column,  becoming  the  dorsal  or 
"  posterior  "  surface  of  human  anatomy.  The  oesophageal  or 
cephalic  end  is  placed  to  the  left  of  the  median  line,  while  the 
caudal  or  pyloric  end  is  situated  on  the  right  side  (Figs.  169 
and  170). 

The  original  ventral  border,  now  the  "  lesser  curvature "  or 
"upper  border,"  looks  cephalad  and  to  the  right,  toward  the 
caudal  surface  of  the  liver,  while  the  original  dorsal  border,  as  the 
" greater  curvature "  or  ''lower  border"  is  directed  in  the  main 
caudad  and  to  the  left. 

The  prominence  of  this  border  is  still  further  increased  by  the 
greater  development  of  the  stomach  to  the  left  of  the  oesophageal 


CHANGES  IN  POSITION  OF  STOMACH.  103 

entrance  resulting  in  the  formation  of  the  "fundus"   or  "great 
cul-de-sac." 

This  rotation  of  the  stomach  explains  the  asymmetrical  position 
of  the  vagus  nerve  in  the  adult,  the  left  side  of  the  embryonic 
stomach,  innervated  by  the  left  vagus,  becoming  the  "anterior  " 
surface  of  adult  descriptive  anatomy  and  vice  versa. 

It  will  be  readily  appreciated  that  a  comparatively  flat  organ 
like  the  stomach,  will,  as  long  as  it  occupies  a  sagittal  position, 
with  right  and  left  surfaces,  help  to  divide  the  upper  part  of  the 
abdominal  cavity  to  a  certain  extent  into  a  right  and  left  half,  even 
if  the  peritoneal  connections  of  the  organ  are  left  out  of  considera- 
tion. As  soon,  however,  as  the  above-described  changes  in  posi- 
tion take  place  and  the  surfaces  of  the  stomach  are  directed  ven- 
trad  and  dorsad,  the  relative  arrangement  and  extent  of  this 
right  and  left  abdominal  space  becomes  altered  by  the  different 
disposition  of  the  septum,  i.  e.,  the  stomach.  The  original  right 
side  of  the  organ  is  now  directed  dorsad,  and  the  rotation  of  the 
organ  has  created  a  space  between  this  dorsal  or  "posterior" 
surface  of  the  stomach  and  the  background  of  the  abdominal 
cavity,  which  is  the  inception  of  the  "  lesser  peritoneal  cavity  " 
or  retrogastric  space.  We  will  find  that  this  space  becomes  well 
defined  and  circumscribed  by  the  peritoneal  connections  of  the 
stomach,  but  we  will  realize,  even  at  this  stage,  that  the  dorsal 
surface  of  the  stomach  will  form  a  part  of  the  general  ventral 
wall  of  the  lesser  peritoneal  space. 

On  the  other  hand,  the  partial  division  of  the  abdomen  into  a 
right  and  left  half,  effected  by  the  stomach  in  its  primitive  sagit- 
tal position,  disappears  after  rotation  of  the  organ.  We  now  pass 
uninterruptedly  from  left  to  right  across  the  ventral  (original  left) 
surface  of  the  stomach. 

B.  Changes  in  the  Direction  and  Extent  of  the  Dorsal  Mesogastrium. 

The  effects  of  the  altered  position  of  the  stomach  on  the  dispo- 
sition of  the  abdominal  space  have  just  been  considered  in  rela- 
tion to  the  organ  itself,  without  reference  to  its  natural  connec- 


104  ANATOMY  OF  THE  PERITONEUM. 

tions  with  the  parietes  and  with  adjacent  viscera.  Their  true  sig- 
nificance and  their  influence  on  the  adult  anatomical  arrange- 
ment of  the  abdomen  is,  however,  only  appreciated  when  the 
changes  in  the  arrangement  of  the  peritoneal  membrane  which 
they  involve,  are  taken  into  account. 

The  dorsal  mesogastrium  changes  more  than  any  other  portion 
of  the  peritoneum  in  the  course  of  development.  It  not  only 
becomes  displaced  and  altered  in  direction  by  the  rotation  of  the 
stomach,  but  in  addition  it  grows  so  extensively  that  it  finally 
hangs  down  like  an  apron  over  the  entire  mass  of  small  intestines, 
forming  the  great  omentum. 

If  we  begin  with  the  primitive  disposition  of  the  sagittal  stomach 
and  dorsal  mesogastrium  shown  in  Fig.  171  it  will  be  observed  that 
both  structures  together  actually  divide  the  dorsal  portion  of  the 
abdominal  cavity  into  symmetrical  right  and  left  halves  (Fig.  172). 

After  rotation  of  the  stomach  (Fig.  173)  the  mesogastrium  loses 
its  original  sagittal  direction.  It  follows  the  altered  position  of 
the  original  dorsal  border  of  the  stomach,  which  has  now  become 
the  caudal  margin  or  "greater  curvature,"  by  turning  caudad  and 
to  the  left,  being  at  the  same  time  considerably  elongated.  This 
occurs  during  the  second  month.  Hence  the  dorsal  mesogastrium, 
after  leaving  the  vertebral  column,  turns  ventrad  and  to  the  left 
to  reach  its  gastric  attachment  along  the  greater  curvature.  This 
is  the  first  indication  of  the  formation  of  the  great  omental  or 
epiploic  bursa. 

The  stomach  is  here  considered  as  developing  in  situ  and  as  in- 
fluencing by  its  growth  and  change  of  position  the  arrangement 
and  direction  of  the  peritoneal  layers  with  which  it  is  connected. 
As  a  matter  of  fact  it  is  well  to  note  that  the  stomach  at  first  lies 
above  the  primitive  diaphragm  or  septum  transversum,  migrating, 
however,  at  an  early  period  into  the  subhepatic  abdominal  posi- 
tion. This  migration  produces  a  corresponding  increase  in  the 
length  of  the  oesophagus  (Fig.  34)  and  the  stomach,  in  conse- 
quence of  this  change  in  position,  acquires  its  ventral  and  dorsal 
mesogastrium.     For   the  purpose  of  explaining  the  adult  peri- 


PLATE    LXXXI. 


STOMACH 


DORSAL 

ME^OGAS- 

TRIUM 


PRIMITIVE 
PARIETAL 
PERITONEUM 
KIDNEY 


Fig.  171.— Schematic  representation  of  dorsal  mesogastrium  before  rotation  of  stomach. 


VENTR 
MESOGA 

TRIUM    <FA 
CI  FORM    LI 

VENTRAL    MES 
GASTRIU 

'gastr 

HERAT 
OMENTU 


UMBILIC 
CO 


DORSAL    MESO- 
GASTRIUM 


STOMACH 


UMBILICAL 
LOOP   OF 
INTESTINE 

MESENTERY 


Fig.   172. — Semi-(liagi<iuii...aio  representation  of  mesogastrium   iu 
human  embrvo  of  the  sixth  week.     (KoUniann.) 


PLATE    LXXXII. 


STOMACH 

X 


^= 

¥ 

SwM 

^^IB 

w 

Msvmm 

WimKSKsBmSmf^^ 

\^^ 

^ 

^^■-v 

V^ 

^^li*^ 

Figs.  173-175. — Schema  of  dorsal  mesogastrium  after  rotation  of  stomach. 
Fig.  173. — Early  stage. 


^-s 

-z^^^ 

^ 

X 

/^ 

IP 

V 

\C^ 

^ 

^/ 

Fig.  174. — Later  stage,  extension  of  mesogastrium  beyond  stom- 
ach to  left,  with  fundus  of  blind  retrogastric  pouch  thus  created  at  X. 


/^^H 

■&>- 

f^^ 

P^ 

X 

$^ 

::> 

Fig.  175. — After  adhesion  over  area  of  dotted  line  between  dorsal 
mesogastrium  and  ])rimitive  parietal  jjeritoneum.  Secondary  line  of 
transition  from  dorsal   mesogastrium  to  parietal  peritoneum  at  X. 


PLATE    LXXXIII. 


MESODUOD- 
ENUM 


DORSAL 
MESOGAS- 
TRIUM 
VENTRAL 
MESOGAS- 
TRIUM    Dt- 
VIDED 
ALONG 
LESSER 
CURVA- 
TURE 

OMENTAL 
BURSA 


Fig.  17G. — Schematic  ventral  view  of  stomach,  duodenum, 
and  dorsal  mesogastrium,  after  rotation  of  stomach  and  ex- 
tension of  omental  bursa  caudad  beyond  greater  curvature  of 
stomach.  The  ventral  mesogastrium  is  detached  along  the 
lesser  curvature. 


DORSAL    MESO- 
GASTRIUM 
VENTRAL    MESOGAS- 
TRIUM    FORMING 
GASTRO-HEPATIC 
OMENTUM 


HEPATIC    DUCT 


MESODUODCNUM 

WITH    PANCREATIC 

BUDS      BETWEEN 

LAYERS 


TRANSV.    COLON 


ASC.    MESOCOLON 
ASC.    COLON 


APPENDIX 


VITELLO- 
INTESTINAL 


CESOPHAGUS 


DORSAL  MESO- 
GASTRIUM 
FORMING 
GREAT 
OMENTUM 


DUODENO- 
JEJUNAL 
JUNCTION 


OESC.    COLON 


DESC.    MESO- 
COLON 


Fig.  177. — Semi-diagrammatic  representation  of  peritoneal  membrane 
in  human  embryo.     (After  KoUmann.) 


PLATE    LXXXIV. 


STOMACH 


DORSAL  MESOGAS- 

TRIUM     FORMING 

VENTRAL    LAYERS 

OF   OMENTUM 


CAVITY    OF 

OMENTAL 

BURSA 


PRIMITIYE 
PARIETAL 
PERITONEUM 


DORSAL  MESOGAS- 
TRIUM       FORMING 
DORSAL       LAYERS 
OF   OMENTUM 


Fig.  178. — Schematic  sagittal  section  through  stomach  and  dorsjil 
mesogastrium,  after  rotation  and  formation  of  omental  bursa. 


SECONDARY  PARIETAL 
PERIT.    DERIVED     FROM 

ORIGINAL  RIGHT  LAYER 
OF  DORSAL  MESOGAS- 
TRIUM 


DORSAL    MESOGAS- 
TRIUM      FORMING 
VENTRAL     LAYERS 
OF   OMENTUM 

CAVITY    OF 

OMENTAL 

BURSA 


AREA    OF    ADHESION 
BETW.    PRIMITIVE 
PARIETAL     PERIT. 
ANDORIGINAL  LEFT 
LAYER    OF    DORSAL 
MESOGASTRIUM 

KIDNEY 


DORSAL    MESOGAS- 
TRIUM      FORMING 
DORSAL      LAYERS 
OF    OMENTUM 


Fig.  179. — Schematic  sagittal  section  through  stomach  and  dorsal  meso- 
gastrium after  adhesion  to  prerenal  parietal  xieritoneum. 


PLATE    LXXXV. 


STOMACH 

GASTHO-SPLENIC     SEGMENT  OF 

DORSAL      MESOGASTR.      WITH     A. 

GAGTRO-EPIPLOICA    SINISTRA 

SPLEEN 

VERTEBRO-SPLENIC 

SEGMENT  OF  DORSAL 

MESOGASTR.       WITH 

SPLENIC    ART. 


Fig.  180. — Schematic  transverse  section  of  the  abdomen,  showing  early  stage  of  development 
of  spleen  from  extreme  left  end  of  dorsal  mesogastric  pouch. 


SPLEEN 

GASTRO-SPLENIC  OMENTUM 
WITH  GASTRIC  BRANCHES 
OF  SPLENIC  ART. 
SECONDARY  PARIETAL  PER  IT. 
DERIVED    FROM    MESOGASTR 

LIENO-RENAL 
PERIT.    FOLD 


PARIETAL    PERIT. 


STOMACH 


AORTA    AND 
ROOT  OF 
DORSAL 
MESOGAS- 
TRIUM 


R.    KIDNEY 


Fig.  181. — Schematic  transverse  section  of  the  abdomen,  showing  later  stage  of  development 
of  spleen  and  arrangement  of  peritoneum  after  adhesion  of  dorsal  layer  of  mesogastrium  and 
primitive  prerenal  parietal  peritoneum. 


CUT  EDGE 
OF  GRE*T 
OMENTUM 

DUODENUM 


Fig.  182. — Part  of  the  abdominal  viscera  of  child,  two  years  old,  hardened  in  situ  and 
removed  |from  body.  The  great  omentum  has  been  detached  along  the  line  of  the  transverse 
colon.     (Columbia  University,  Study  Collection.) 


PLATE    LXXXVI. 


SECONDARY     PARIETAL 

PERIT.    OF  LESSER   SAC 

DERIVED    FROM    MESO- 

GASTRIUM 

TWO     LAYERS    OF    GAS 

TRO-SPLENIC  OMENTUM 

CUT    EDGE    OF    LIENO- 

RENAL    FOLD 

TAIL  OF    PANCREAS 

CUT   EDGE    OF   GREAT 
OMENTUM 


GASTRIC     SURFACE 
OF    SPLEEN 
SURFACE    COVERED 
BY    LESSER    SAC 
GASTRO-SPLENIC 
OMENTUM 

REFLECTION  TO  DOR- 
SAL WALL  OF  LESSER  SAC 
REFLECTION  TO  KIDNEY 
AND  DIAPHRAGM  (LIENO- 
RENAL    LIG.) 

TAIL   OF    PANCREAS 

RENAL   SURFACE 
OF   SPLEEN 


Fig.  183.— The  same  preparation  with  the  spleen  removed,  showing  lines  uf  peritoneal  reflec- 
tion on  mesial  surface  of  the  organ. 


DORSAL  SURFACE    OF   STOMACH 


LEFT  PANCREATICO- 
GASTRIC  FOLD  SEPA- 
RATING HEPATIC  AN- 
TRUM OF  LESSER  SAC 
FROM  BURSA  OMEN- 
TALIS 

R      KIDNEY     HEPATIC 
SURFACr 

COLIC  AREA  or 

DESC.   DUODENUN^ 

COLIC    AREA   OF 

R.    KIDNEV 


MESOCOLIC    AREA 
OF    R.    KIDNEY 

INFRACOLIC    SEG- 
MENT OF  DESC. 
DUODENUM 


DEXTRO-MESEN- 

TERIC  SEGMENTOF 

TRANSV.    DUOD. 


LEFT    EXTREMITY    OF 
LESSER    PERITONEAL 
SACTOUCHING  HILUS 
OF  SPLEEN 
SPLEEN 


VENTRAL    SURFACE 
OF    PANCREAS 
ATTACHMENT    OF   TRANSV 
MESOCOLON    TO    VENTRAL 
MARGIN    OF    PANCREAS 
CAUDAL    SURFACE 
OF    PANCREAS 


LEFT     KIDNEY 


ASC.     DUODENUM 

MESENTERY    CROSSING 
TRANSV.     DUODENUM 
ATTACHMENT    OF 
DESC.    COLON 

SI  NISTRO- MESENTERIC 
SEGMENT    OF    TRANSV 
DUODENUM 


Fig.  184.—Upper  abdominal  viscera  of  adult  human  subject,  hardened  in  situ,  with  liver  and 
coJon  removed  and  stomach  turned  up.     (Columbia  University,  Study  Collection.) 


PLATE   LXXXVII. 


LEFT  HEPATIC 

DUCT 

RIGHT  HEPATIC 

DUCT 


GALL-BLADDER 


DORSAL 
PANCREAS 


VENTRAL 
PANCREAS 


DUODENUM 


Fig.  185. — Pancreatic  and  hepatic  buds  of  human  embryo  of  four  weeks.     (Kollmann.) 


VENTRAL 
PANCREAS 


DORSAL 
PANCREAS 


STOMACH 


Fig.  186. — Pancreatic  buds  of  human  embryo  of  five  weeks.     (Kollmann,  after  Hamburger.) 


DUODENUM 
BILE-DUCT 

VENTRAL 
PANCREAS 
AND    PAN- 
CREATIC 
DUCT 

DUCT   OF 
SANTORINI 


FUSION  OF  THE  TWO  PANCREATIC  BUDS 
CORRESPONDING  TO  ADULT  CONNEC- 
TION OF  DUCT  OF  SANTORINI  AND 
MAIN    PANCREATIC    DUCT 


DORSAL 
PANCREAS 


STOMACH 


Fig.  187. — Pancreatic  buds  of  human  embryo  of  six  weeks.     (Kollmann,  after  Hamburger.) 


> 

X 

X 
X 

< 


DIRECTION  AND  EXTENT  OF  THE  DORSAL  MESOGASTRWM.    105 

toneal  relations  of  the  organ  it  is,  however,  more  convenient  to 
regard  the  stomach  as  an  abdominal  organ  from  the  beginning 
and  to  deal  with  the  subsequent  changes  in  position  from  this^ 
standpoint.  The  inaccuracy  is  slight  and  renders  the -comprehen- 
sion of  the  succeeding  stages  easier. 

It  will  be  noticed  (Fig.  173)  that  the  rudimentary  retro-gastric 
space  or  "lesser  peritoneal  sac"  is  bounded  ventrally  by  the  dor- 
sal (the  primitive  right)  surface  of  the  stomach,  while  its  dorsal 
boundary  is  furnished  by  the  ventral  (originally  right)  layer  of 
the  dorsal  mesogastrium. 

In  the  primitive  condition,  therefore,  dorsal  mesogastrium  and 
stomach  form  together  a  straight  line  sagittal  in  direction  and 
placed  in  the  median  plane  of  the  body.  As  the  result  of  the 
developmental  changes  above  outlined  this  straight  line  becomes 
bent  at  the  point  where  the  mesogastrium  reaches  the  stomach 
(Fig.  173,  x).  The  two  component  elements  of  the  line  (stomach 
and  mesogastrium)  hinge  on  each  other  here,  and  the  angle  which 
they  form  opens  to  the  right. 

The  changes  which  are  to  be  observed  in  the  later  stages  depend 
principally  upon  a  peculiar  feature  characteristic  of  the  develop- 
ment of  the  dorsal  mesogastrium.  This  feature  consists  in  the 
extreme  redundancy  of  the  membrane  which  grows  out  of  pro- 
portion to  the  requirements  of  its  visceral  connections,  and  to  a 
certain  extent  becomes  independent  of  the  direct  mechanical  pur- 
pose of  carrying  blood  vessels  to  the  viscera.  Hence  in  a  trans- 
verse section  at  this  period  (Figs.  174  and  175)  the  mesogastrium 
no  longer  passes  in  a  direct  line  between  its  points  of  attachment, 
viz.  the  greater  curvature  of  the  stomach  and  the  vertebral  col- 
umn, but  extends  beyond  the  stomach  to  the  left.  We  will 
appreciate  the  significance  of  this  extensive  growth  of  the  meso- 
gastrium especially  in  considering  the  development  of  the  spleen 
and  pancreas.  For  the  present  it  will  suffice  to  note  (Figs.  174 
and  175)  that  the  growth  has  carried  the  mesogastrium  well  to 
the  left  of  the  stomach,  consequently  the  retrogastric  space  is  now 
bounded  toward  the  left  by  the  bend  which  the  original  right  leaf 


106  ANATOMY  OF  THE  PERITONEUM. 

of  the  primitive  sagittal  mesogastrium  takes  in  order  to  reach  its 
gastric  attachment.  The  retrogastric  space  therefore  terminates 
toward  the  left  in  a  blind  pocket  formed  by  this  reduplication  of 
the  mesogastrium. 

One  more  factor  is  to  be  taken  into  consideration,  namely  the 
tendency,  already  noted,  of  peritoneal  surfaces  to  become  adherent 
to  each  other.  Such  adhesion  involves  the  apposed  surfaces  of 
the  mesogastrium  and  of  the  primitive  parietal  peritoneum  to 
the  left  of  the  vertebral  column.  The  dorsal  (original  left)  layer 
of  the  mesogastrium  adheres  to  the  parietal  peritoneum  covering 
the  left  side  of  the  abdominal  background  and  the  cephalic  por- 
tion of  the  ventral  surface  of  the  left  kidney  up  to  the  end  of 
the  blind  pouch  which  forms  the  extreme  left  limit  of  the  retro- 
gastric  space.  Hence,  after  this  process  of  adhesion  is  completed^ 
the  dorsal  wall  of  the  retrogastric  space  is  lined  by  secondary 
parietal  peritoneum  covering  the  left  kidney  (original  right  leaf 
of  primitive  mesogastrium)  (Fig.  175).  We  obtain  (Fig.  175  at 
x)  an  apparent  continuity  of  the  parietal  peritoneum  with  that 
portion  of  the  mesogastrium  which,  derived  from  the  original 
left  layer  of  the  membrane,  appears  now  to  extend,  as  the  ven- 
tral one  of  two  layers,  between  the  stomach  and  the  abdominal 
parietes  near  the  lateral  border  of  the  left  kidney.  (Primitive 
gastro-splenic  omentum.) 

It  should  be  remembered  that  the  disposition  of  the  peritoneum 
just  indicated  is  modified  by  the  development  of  the  pancreas 
and  spleen,  both  of  which  organs  are  intimately  associated  with 
the  mesogastrium.  The  foregoing  statements  and  diagrams  are 
therefore  merely  given  for  the  purpose  of  affording  a  general  view 
of  the  extent,  growth  and  changes  of  the  dorsal  mesogastrium 
before  proceeding  to  consider  the  development  of  the  pancreas 
and  spleen  in  and  from  the  membrane  itself 

In  the  view  directly  from  in  front  the  redundancy  of  the  peri- 
toneum forming  the  mesogastrium  is  shown  in  Figs.  176  and  177. 
Just  as  the  membrane  extends  further  to  the  left  than  required  by 
its  visceral  connection  with  the  stomach,  so  the  downward  growth 


DIRECTION  AND  EXTENT  OF   THE  DORSAL  MESOGASTRIUM.    107 

exceeds  the  demand  made  by  the  rotation  of  the  attached  border 
(greater  curvature)  caudad  and  to  the  left.  The  mesogastriura, 
forming,  as  it  now  does,  the  great  omentum,  enlarges  in  descend- 
ing toward  the  transverse  colon  (Fig.  177).  The  bag  thus  formed 
can  be  distended  with  air  in  a  foetus  of  from  8  to  9  cm.  vertex- 
coccygeal  measure,  as  shown  in  the  figure.  Consequently  in  sagit- 
tal section  the  membrane  is  seen  to  extend  caudad  beyond  the 
level  of  the  greater  curvature,  and  must  turn  on  itself  and  pass 
again  cephalad  in  order  to  reach  the  stomach  (Fig.  178).  By 
reason  of  this  excessive  growth  the  limits  of  the  primitive  retro- 
gastric  space  are  enlarged,  not  only  toward  the  left,  but  more 
especially  in  the  caudal  direction.  The  bend  made  by  the  meso- 
gastrium  in  returning  to  the  stomach  forms  the  blind  extremity 
of  a  pouch  which  continues  the  retrogastric  space  caudad  beyond 
the  stomach,  and  whose  dorsal  and  ventral  walls  are  formed  by 
the  reduplicated  mesogastrium.  This  pocket  or  pouch  consti- 
tutes the  omental  or  epiploic  bursa  of  the  lesser  peritoneal  cavity, 
for  the  great  omentum  is  the  direct  product  of  this  redundant 
growth  of  the  mesogastrium  caudad.  It  will  be  observed  that 
the  great  omentum  is  made  up  of  four  peritoneal  layers,  the  fold- 
ing of  the  double-layered  mesogastrium  naturally  producing  tliis 
result.  The  first  or  ventral  and  the  fourth  or  dorsal  layer  are 
derived  from  the  original  left  layer  of  the  primitive  sagittal  meso- 
gastrium ;  the  intermediate  second  and  third  layers,  separated 
from  each  other  at  this  stage  by  the  cavity  of  the  omental  bursa, 
are  products  of  the  primitive  right  leaf  of  the  mesogastrium. 
Since  the  entire  retrogastric  space  with  its  extension^  becomes  the 
"  lesser  cavity  "  of  the  human  adult  peritoneum,  it  will  be  seen 
that  its  serous  membrane  is  derived  from  the  original  right  leaf 
of  the  mesogastrium  (second  and  third  omental  layers).  After 
the  above-described  adhesion  of  the  mesogastrium  to  the  parietal 
peritoneum  overlying  the  ventral  surface  of  the  left  kidney,  the 
membrane  would  be  traced  in  sagittal  section  (Fig.  179)  from  the 
dorsal  surface  of  the  stomach  caudad,  lining  the  interior  of  the 
omental  bursa  (second  layer)  to  the  turn  or  blind  end  of  the 


108  ANATOMY  OF   THE  PERITONEUM. 

pouch ;  thence  cephalad  as  the  third  omental  layei*,  forming  the  dor- 
sal wall  of  the  epiploic  bursa,  to  invest,  as  secondary  parietal  perito- 
neum, the  cephalic  segment  of  the  ventral  surface  of  the  left  kidney. 

0.  Development  of  Spleen  and  Pancreas  in  the  Dorsal  Mesogastrinm 
and  Changes  in  the  Disposition  of  the  Great  Omentum. 

In  order  to  obtain  a  correct  conception  of  the  adult  human 
conditions  it  is  finally  necessary  to  consider  the  development  of 
the  spleen  and  pancreas  in  their  connection  with  the  dorsal  meso- 
gastrinm and  to  note  the  changes  which  are  produced  by  adhesion 
of  portions  of  the  great  omentum  to  adjacent  serous  surfaces.  It 
will  be  advisable  to  discuss  these  subjects  at  first  separately,  and 
to  subsequently  combine  all  the  facts  in  an  attempt  to  gain  a  cor- 
rect impression  of  their  share  in  determining  the  disposition  of 
the  adult  human  peritoneum. 

1.  Development  of  Spleen. — The  spleen  develops  from  the  meso- 
derm between  the  layers  of  the  dorsal  mesogastrinm,  near  its  point 
of  accession  to  the  greater  curvature,  in  the  region  of  the  subse- 
quent fundus.  It  has  therefore,  like  the  stomach,  originally  free 
peritoneal  surfaces.  After  rotation  of  the  stomach  the  organ  lies 
between  the  two  layers  of  the  membrane  at  the  extreme  left  end 
of  the  retrogastric  space  (Fig.  180). 

Vascular  Connections. — The  splenic  artery  accedes  to  the  mesal  sur- 
face of  the  spleen  from  the  vessel  which  originally  passed  directly 
to  the  dorsal  border  (subsequent  greater  curvature)  of  the  stomach, 
between  the  layers  of  the  mesogastrinm. 

With  the  further  growth  of  the  spleen  the  segment  of  this  vessel 
situated  between  its  origin  from  the  coeliac  axis  and  the  hilum  of 
the  spleen  becomes  relatively  larger,  forming  the  adult  splenic 
artery,  while  the  continuation  of  the  original  vessel  to  the  greater 
curvature  of  the  stomach  appears  now  as  a  branch  of  the  splenic 
artery,  viz.,  the  arteria  gastro-epiploica  sinistra. 

Through  the  development  of  the  spleen  the  dorsal  mesogastrinm 
has  been  subdivided  into  a  proximal  longer  vertebro-splenic,  and 
a  distal  shorter  gastro-splenic  segment.     The  former,  as  we  have 


VASCULAR   CONNECTIONS.  109 

seen,  loses  its  identity  as  a  free  membrane  in  the  human  adult,  by 
fusing  with  the  parietal  peritoneum  investing  the  ventral  surface 
of  the  left  kidney.  Hence,  after  this  adhesion  hasltaken  place,  the 
splenic  artery  courses  from  the  coeliac  axis  to  the  spleen  behind 
peritoneum  which  functions  as  part  of  the  general  parietal  mem- 
brane, but  which  is  derived  from  the  original  right  leaf  of  the 
proximal  vertebro-splenic  segment  of  the  primitive  mesogastrium 
(Fig.  181).  On  the  other  hand  the  distal  segment  of  this  mem- 
brane, beyond  the  spleen,  remains  free,  carrying,  as  the  gastro- 
splenic  omentum,  the  left  gastro-epiploic  artery  between  its  layers 
from  the  splenic  artery  to  the  greater  curvature  of  the  stomach. 

The  lateral  limit  of  the  area  of  adhesion  between  mesogastrium 
and  parietal  peritoneum  is  situated  along  the  lateral  border  of  the 
left  kidney.  Hence,  in  the  final  condition  of  the  parts,  the  main 
splenic  vessels  at  the  hilum  are  situated  between  two  peritoneal 
layers  of  which  the  ventral  (Fig.  181)  appears  as  the  parietal 
peritoneum  forming  the  dorsal  wall  of  the  retro-gastric  space, 
while  the  dorsal  layer  (Fig.  181)  forms  a  reflection  from  the  mesal 
surface  of  the  spleen,  along  the  dorsal  margin  of  the  hilum,  to  the 
adjacent  lateral  border  of  the  left  kidney  (lieno-renal  ligament) 
and  to  the  diaphragm.  At  this  point  of  adhesion  subsequently 
firmer  strands  of  connective  tissue  develop  in  the  serous  redupli- 
cation forming  the  ligamentum  phrenico-lienale  of  systematic  anat- 
omy. This  process  of  adhesion  takes  place  during  the  second 
half  of  intra-uterine  life.  A  connection  with  the  colon,  produced 
by  adhesion  of  the  mesogastrium  to  the  splenic  flexure  of  the 
large  intestine,  forms  the  adult  lig.  colico-lienale,  while  a  similar 
adhesion  between  great  omentum,  transverse  mesocolon  and 
phrenic  parietal  peritoneum  just  caudad  of  the  spleen,  gives  rise  to 
the  colico-phrenic  or  costo-colic  "  supporting  "  ligament  of  the  spleen. 

On  the  other  hand,  the  ventral  one  of  the  two  layers  constitut- 
ing the  gastro-splenic  omentum  and  including  between  them  the 
left  gastro-epiploic  artery,  is  formed  by  the  distal  part  of  the 
primitive  left  layer  of  the  mesogastrium,  while  the  dorsal  layer 
of  the  same  fold  is  the  portion  of  the  primitive  right  layer  be- 


110  ANATOMY  OF  THE  PERITONEUM. 

yond  the  spleen,  which  has  not  been  converted  into  secondary 
parietal  peritoneum,  but  forms  now  part  of  the  ventral  wall  of 
the  lesser  peritoneal  sac  between  the  spleen  and  the  stomach 
(Fig.  181)  (lig.  gastro-lienale).  Since,  therefore,  the  gastro-splenic 
omentum  is  a  specialized  part  of  the  fully-developed  dorsal  meso- 
gastrium,  and  since  we  have  seen  that  the  great  omentum  is 
formed  directly  by  the  excessive  growth  of  this  membrane  cau- 
dad,  it  is  not  difficult  to  understand  why  in  the  adult  human 
subject  the  ventral  layer  of  the  gastro-splenic  omentum  is  di- 
rectly continuous  with  the  ventral  layer  of  the  great  omentum 
along  the  greater  curvature  of  the  stomach  to  which  both  are 
attached.  The  dorsal  layer  of  the  gastro-splenic  omentum  would, 
in  the  same  wa}^  be  continuous  with  the  second  layer  of  the  great 
omentum,  lining  the  ventral  wall  of  the  omental  bursa,  if  it  were 
not  for  the  fact  that  in  the  adult  adhesions  usually  obliterate  the 
cavity  of  the  bursa. 

Fig.  182  shows  the  stomach,  left  kidney,  spleen  and  splenic 
flexure  of  the  colon  hardened  in  situ  and  removed  from  the  body 
of  a  two-year-old  child.  The  great  omentum  has  been  divided 
along  the  line  of  adherence  to  the  transverse  colon. 

In  Fig.  183  the  spleen  has  been  removed  from  the  preparation 
by  division  of  its  peritoneal  and  vascular  connections,  and  is 
shown  in  its  mesal  aspect  (gastric  and  renal  surfaces,  intermediate 
margin  and  hilum).  It  will  be  seen  that  the  peritoneal  reflections  are 
arranged  in  the  form  of  two  concentric  elliptical  lines.  The  two 
ventral  lines  form  the  gastro-splenic  omentum  and  correspond  to 
the  reflection  of  the  peritoneum  from  spleen  to  left  end  of  stomach 
carrying  the  gastric  branches  derived  from  the  splenic  artery. 
The  third  line  from  before  backwards  results  from  the  division  of 
the  secondary  parietal  peritoneum  of  the  lesser  sac,  covering 
splenic  artery,  and  ventral  surface  of  pancreas  and  derived  from 
the  dorsal  mesogastrium ;  while  the  most  dorsal  fourth  line 
represents  the  divided  reflection  of  the  peritoneum  from  the  renal 
surface  of  spleen  to  lateral  border  of  left  kidney  and  diaphragm 
(lig.  lieno-renale). 


DEVELOPMENT  OF  THE  PANCREAS.  Ill 

Between  the  second  and  third  lines  of  peritoneal  reflection  ap- 
pears the  portion  of  the  mesal  surface  of  the  spleen  in  contact  with 
and  invested  by  the  extreme  left  end  of  the  lesser  peritoneal  sac. 

Fig.  184,  taken  from  an  adult  human  subject  with -the  viscera 
hardened  in  situ,  shows  the  left  or  splenic  extension  of  the  lesser 
peritoneal  cavity. 

2.  Development  of  the  Pancreas. — The  pancreatic  gland  is  derived 
from  the  hypoblast  of  the  enteric  tube.  The  secreting  epithelium 
and  that  lining  the  ducts  of  the  adult  gland  is  formed  by  bud- 
ding and  proliferation  of  the  intestinal  epithelium.  The  gland 
develops  primarily  from  two  outgrowths  which  are  at  first  sepa- 
rate and  distinct  from  each  other. 

1.  The  proximal  and  dorsal  bud  grows  directly  from  the  hypo- 
blast lining  the  duodenum  immediately  beyond  the  pyloric  junc- 
tion. 

In  embryos  of  8  mm.  (four  weeks)  (Fig.  185)  it  appears  as  a 
small  spherical  outgrowth  connected  by  a  slightly  narrower  stalk 
with  the  epithelial  intestinal  tube. 

2,  The  distal  and  ventral  outgrowth  is  separated  from  the  pre- 
ceding and  is  from  the  beginning  closely  connected  with  the 
similar  embryonic  outgrowth  from  the  enteric  tube  which  is  to 
form  the  liver.  This  portion  of  the  pancreas  is,  strictly  speak- 
ing, derived  primarily  from  the  epithelium  of  the  primitive 
hepatic  duct  and  not  directly  from  the  duodenum.  This  pri- 
mary arrangement  of  the  gland,  being  formed  of  two  main  col- 
lections of  budding  hypoblastic  cells,  corresponds  to  the  adult 
system  of  the  pancreatic  excretory  ducts.  The  proximal  or  dor- 
sal outgrowth  furnishes  that  portion  of  the  head  of  the  gland 
whose  excretory  system  terminates  in  the  secondary  pancreatic 
duct  or  duct  of  Santorini,  while  the  distal  (ventral)  outgrowth 
includes  within  its  area  the  termination  of  the  principal  pancre- 
atic duct  or  canal  of  Wirsung,  which  is  closely  connected  with 
the  end  of  the  common  bile-duct  at  the  intestinal  opening  com- 
mon to  both  (Figs.  186-187).  The  method  of  union  of  the  two 
pancreatic  outgrowths  and  their  respective  share  in  building  up 


112  AMATOMY  OF  THE  PERITONEUM. 

the  adult  gland  explains  the  usual  adult  arrangement   of  the 
excretory  system  and  its  variations. 

In  the  embryo  of  five  weeks  (Fig.  186)  the  two  portions  have 
grown  in  length.  The  dorsal  or  proximal  outgrowth,  developing 
between  the  layers  of  the  mesoduodenum,  is  at  this  time  the  larger 
of  the  two,  composed  of  a  number  of  glandular  vesicles  clustered 
around  the  stalk  represented  by  the  parent  duct. 

The  distal  or  ventral  pancreatic  growth,  connected  with  the 
liver  di  *-,  is  as  yet  small  and  presents  only  a  few  vesicular  ap- 
pendages. The  duct  of  this  portion  empties  in  common  with  the 
hepatic  duct  into  the  duodenum. 

In  embryos  of  the  sixth  to  seventh  week  (Fig.  187),  the  two 
glandular  outgrowths  have  become  connected  with  each  other  at  a 
point  which  corresponds  exactly  to  the  divergence  of  the  duct  of 
Santorini  from  the  main  pancreatic  duct  (canal  of  Wirsung)  in  the 
adult  gland  (Fig.  188). 

The  secondary  pancreatic  duct  (of  Santorini)  of  the  adult  corre- 
sponds to  that  section  of  the  proximal  or  larger  embryonic  out- 
growth situated  between  the  intestine  and  the  point  where  the 
two  glandular  diverticula  fuse  with  each  other.  Hence  the  canal 
of  Wirsung  in  the  adult  is  a  compound  product.  It  includes  the 
duct  system  developed,  in  connection  with  the  bile  duct,  in  the 
head  of  the  gland,  forming  the  intestinal  termination  of  the  main 
duct.  Its  distal  body  portion  on  the  other  hand  is  derived  from 
the  duct  system  of  the  originally  larger  proximal  outgrowth,  in- 
cluding the  entire  peripheral  portion  which  has  become  secondarily 
added  to  the  duct  of  tne  ventral  outgrowth  to  form  together  with 
it  the  canal  of  Wirsung.  On  the  other  hand  the  proximal  portion 
of  the  duct  system  of  this  originally  larger  part  becomes  second- 
arily differentiated  as  the  duct  of  Santorini. 

Fig.  188  shows  the  normal  adult  arrangement  of  the  pancreatic 
and  biliary  ducts  in  a  corrosion  preparation  of  the  canal. 

The  duct  of  Santorini  in  this  case  opened  by  a  separate  orifice 
into  the  duodenum  above  the  common  opening  of  the  biliary  and 
pancreatic  ducts  (cf  p.  113). 


PLATE    LXXXIX. 


DUODENUM 


COMMON 
BILE-DUCT 


DIVERTICULUM 

VATERI     'COM- 

K'.CN    DUODENAL 

OPENING    OF 

BILIARY     AND 

PANCREATIC 

DUCTS) 


DUCT   OF 
SANTORINI 


MAtN    PANCRE- 
ATIC     DUCT 
CANAL   OF 
WIRSUNG) 


Figs.  1 89-192.— Series  of  schemata  showing  normal  and  variant  adult  types  of  biliary  and 
pancreatic  ducts. 

Fig.  189. — Usual  human  adult  type. 


DUODENUM 

DUCT    OF 
SANTORIN 
ACTING    AS 
MAIN     PAN 

CREATIC 
DUCT 


COMMON 
BILE-DUCT 


PANCREATIC 
DUCT  DEVEL- 
OPED   FROM 
DISTAL    EM- 
BRYONIC 
BUD 


Fig.  190. — Persistence  of  early  embryonal  type. 


PLATE    XC. 


DUODENUM 


COMMON 
BILE-DUCT 


DIVERTICULUM 
VATERI  WITH 
DUODENAL 
OPENING  OF 
BILIARY  AND 
PANCREATIC 
DUCTS 


DUCT   OF 

SANTORINl 

WITHOUT 

DUODENAL 

OPENINC 


main  pancre- 
atic duct 
(canal  of 

WIRSUNG) 


Fig.  191. — Duct  of  Santoriiii  has  no  duodenal  orifice. 


DUODENUM 
DUCT    OF 
SANTORINl 
FORMING 
SOLE    PAN- 
CREATIC 
DUCT 


COMMON 
BILE-DUCT 


Fig.  192. — Duct  of  Santorini  forms  the  only  pancreatic  duct.  Separate  duodenal  openings  of 
biliary  and  pancreatic  ducts,  resulting  from  failure  of  development  of  distal  embryonal  pancre- 
atic bud. 


PLATE    XCI. 


PROBE    IN 
DUODENAL 
OPENING 
OF   DUCT  OF 
SANTOBINI 


PROBE    IN 
OPENING    OF 
DIVERTICULUM 
VATERI  (COM- 
MON   OPENING 
OF    BILIARY 
AND    PANCRE- 
ATIC   DUCTSJ 


Fig.  193.^Mucous  surface  of  human  duodenuuj,  showing  entrance  of  biliary  and 
pancreatic  ducts  and  diverticulum  Vateri.     (Columbia  University  Museum,  No.  1842.) 


Fig.  194. — Adult  human  subject.     Mucous  membrane  of  pyloro-duodeual  junction 
and  of  duodenum.     (Columbia  University  Museum,  No.  1840.) 


PLATE    XCII. 


PANCREATIC 
DUCT 


COMMON 
BILE-DUCT 


DIVERTICU- 
LUM  VATERI 


Fig.  195. — Duodenum,  with  entrance  of  pancreatic 
and  biliary  ducts  and  well-developed  diverticulum  Vateri 
in  the  cassowary,  Casuarms  caauarius.  (Columbia  Uni- 
versity   Museum,  No.  1821.) 


PLATE    XCIII, 


OAI  1  - 

BLADDER 

HEPATIC 

DUCT 

PANCREAS 

C^^i 

COMMON    BILE-DUCT 

RECEIVING   PANCRE 

ATIC    DUCTS         / 

MID-GUT 1 

'  S^  V 

PYLORIC 

C>ECA— C 

n 


-STOMACH 


Fig.  196.— a  portion  of  alimentary  canal  of  Pleurmiectes  maculatus, 
the  flounder,  with  pancreas  attached  to  biliary  duct  and  concealed  in 
the  substance  of  the  liver,  which  has  been  removed.  (Columbia  Uni- 
versity Museum,  No.  1491.) 


DUODENUM 


LOBES  OF 
LIVER 


COMMON 
BILE-DUCT 


PANCREATIC 
DUCT 


Fig.  197.— Pancreas  and  biliary  ducts  of  Bana  esculenta,  frog.     (Wieder- 
sheim,  after  Parker;  both  from  Ecker.) 


PLATE    XCIV. 


CESOPHAGUS 


STOMACH 


POSTCAVA 
DIVIDED  AT 
ENTRANCE 
INTO    SINUS 
VENOSUS 
OF    RIGHT 
AURICLE 

VENTRAL 


f        ^ — BODY- 
WALL 


VENTRAL 

MESOGAS- 

TRIUM 


POSTCAVA 
DIVIDED    AT 
ENTRANCE 
INTO    LIVER 
SPLENIC    V. 


PANCREAS 


GALL- 
BLADDER 


abdominal  v.  in 
free  edge  of 
ventral  meso- 
gastrium 
hepatic    portal 
'mesenteric 


Fig.  198. — Necturus  maculatus,  mud  puppy.  Dissection  of  intestinal 
canal,  liver,  pancreas,  and  spleen,  with  blood-vessels  injected.  (Colum- 
bia University  Museum,  No.  18G3.) 


PLATE    XCV. 


SMALL    PROXI 
MAL  PANCREATIC 
DUCT   JOINING 
HEPATIC    DUCT 


DISTAL  MAIN  PANCREATIC 
DUCT  OPENING  INTO  ASC. 
LIMB  OF  DUODENAL  LOOP 


Fig.  199. — Pancreas  aud  pancreatic  ducts  of  rabbit.     (Nuhn.) 


HEPATIC    DUCT 

PROXIMAL    SMALLER 

PANCREATIC    DUCT 

OECUM 


DISTAL    LARGER 

PANCREATIC 

DUCT 


Fig.  200. — Abdominal  viscera  of  dog,  showing  arrangement  of 
pancreatic  ducts.  (Nuhu.) 


PLATE    XCVI. 


PROBE    IN 
ORIFICE 
OF    MAIN 
PANCRE- 
ATIC DUCT 


DUODENAL 
MUCOSA 

PROBE   IN 
ORIFICE 
OF    BILI- 
ARY 
DUCT 


OESOPHAGUS 


Fig.  201.— Section  of  dog's  stomach,  and    proximal  portion  of  duodenum,    -with 
entrance  of  biliary  and  pancreatic  ducts.     (Columbia  University  Museum,  No.  1822.) 


PLATE    XCVII. 


PANCREAS 


MID-GUT: 
WITH    SUB- 
INTESTINAL 
VEIN    AND 
SPIRAL 
VALVE 


FORE-GUT 


STOMACH 


CONTRACTED 
PYLORIC  SEG- 
MENT  OF 
STOMACH 


Fig.   202. — Alimentary   tract  witli    spleen  and  pancreas  of  Squalus  acanthias,  the  dog-fish. 
(Columbia  University  Museum,  No.  1405.) 


PLATE    XCVIII. 


STOMACH 


PANCREAS 


SPIRAL  INTES- 
TINAL   VALVE 


Fig.  203. — Alimentary  canal  of  Galeus  canis,  dog-siark,  in 
section,  showing  spiral  intestinal  valve.  (Columbia  Univer- 
sity Museum,  No.  1429.) 


PLATE    XCIX. 


Fig.  204. — Alimentary  canal  with  spiral  valve  of  Ceratodus 
forsteri,  the  Australian  lung-fish  (Barramunda).  (Columbia  Uni- 
versity Museum,  No.  1645.) 


o 

Oh 


^   M 

S--S 


S  § 
._5  ft 


U)  0.  u 

1- 
tt) 

1 

1 

1 
1 

1 
1 

1 

1 

g 

c 

!2; 

^ 

a 

j3 

(A, 

s< 

«t-l 

s 

hS 


2  c-- 
'^  ^?--  r%> 


PLATE    CI. 


PYLORUS  —     —      — 


Fig.  207. — Stomach,  duodenum,  and  pyloric  cseca  of  Lophius  piscatorius,  angler. 
(Columbia  University  Museum,  No.  1824.) 


MID-GUT 

PYLORIC   C>eCA 

BILE-DUCT 


CESOPHAGUS 


STOMACH 
PYLORUS 


Fig.   208. — Pleuronecfes   maculatus,   window-pane.      Stomach  and   mid-gut   with 
pyloric  cseca  and  hepatic  duct.     (Columbia  UuivLr.sity  Museum,  No.  1432.) 


ORIFICE  OF 
BILE-DUCT 


Fig.  209. — Pleuronectes   maculatus,   window-pane.      Stomach   and   mid-gut   with 
pyloric  caeca,  in  section.     (Columbia  University  Museum,  No.  1433.) 


PLATE    CII. 


Fig.  210. — Paralichthys  dentatus,  summer  flounder.  Stomach 
and  mid-gut  with  pyloric  cseca  and  liver.  (Columbia  University 
Museum,  No.  1431.) 


COLLECTING 
TUBULES 
FORMED    BY 
JUNCTION 
OF  PYLORIC 
C/ECA 


A  B 

Fig.  211. — Pyloric  cffica  of  Gadns  callarias,  codfish.     (Columbia  University  Museum,  No.  182.5.) 

A.  Bound  together  by  connective  tissue  and  blood-vessels. 

B,  Dissected  to  show  contiuence  of  cseca  to  form  a  smaller  number  of  terminal  tubes  of  larger 
calibre  entering  the  intestine. 


PLATE    cm. 


PYLORIC 
APPENDICES 


ILEO-COLIC 
JUNCTION 


STOMACH 


—     -     SPLEEN 


Fig.  212. — Alimentary  canal  of  Accipenser  sturio,  sturgeon.  Numerous 
pyloric  cseca  are  bound  together  to  form  a  gland-like  organ.  (Columbia  Uni- 
versity Museum,  Nos.  1826,  1827,  and  1828.) 

In  the  smaller  upper  figure  on  the  left  the  stomach,  mid-gut,  and  pyloric 
ca?ca  are  seen  in  section,  showing  the  lumen  of  the  latter  and  their  openings 
into  the  mid-gut. 

The  lower  left-hand  figure  shows  the  mid-  and  end-gut  in  section,  the 
latter  provided  with  a  spiral  mucous  valve. 


PLATE    CIV. 


Fig.  213. — Melamgrammus  xglifinm,  haddock.  Stomach, 
mid-gut,  and  pyloric  cseca ;  spleen.  (Columbia  University 
Museum,  No.  lo98.) 


PYLORIC 
OECA 

PROBES   PASSED 

INTO    INTESTINAL 

ORIFICES  OF 

PYLORIC  CJECA 


STOMACH 


Fig.  214. — Stomach  and  mid-gut  of  Gadiis  callarias,  cod- 
fish, in  section,  showing  intestinal  openings  of  pyloric  caeca. 
(Columbia  University  Museum,  No.  1830.) 


ADULT  ARRANGEMENT  OF  HUMAN  PANCREATIC  DUCTS.        113 

Explanation  of  Adult  Arrangement  of  Human  Pancreatic  Ducts  and  Their 
Variations  Dependent  Upon  the  Embryonic  Development. — The  smaller 
distal  embryonic  outgrowth  is,  as  we  have  seen,  from  its  inception 
in  close  connection  with  the  duodenal  end  of  the  common  bile- 
duct  (Fig.  185). 

The  proximal  outgrowth,  situated  nearer  to  pylorus  and  de- 
rived directly  from  the  duodenal  epithehum,  is  the  larger  and 
forms  the  greater  part  of  the  bulk  of  the  adult  pancreas  (Figs. 
186,  187). 

If,  notwithstanding  this  primitive  arrangement,  the  distal  duct 
(canal  of  Wirsung)  appears  as  the  main  pancreatic  duct  in  the 
adult,  while  the  proximal  (duct  of  Santorini)  is  secondary,  this 
depends  upon  a  union  of  the  products  of  the  two  outgrowths  in 
such  a  manner  that  the  greater  part  of  the  duct  system  of  the 
proximal  and  larger  portion  is  transferred  to  the  distal  duct  to 
form  the  adult  canal  of  Wirsung,  while  the  smaller  segment  of 
the  proximal  duct,  between  its  opening  into  the  duodenum  and 
the  point  of  fusion  of  the  two  outgrowths,  forms  the  adult  secon- 
dary duct  of  Santorini.  This  duct  opens  usually  into  the  duo- 
denum upon  a  small  papilla  situated  about  2.5  cm.  above  the 
common  duodenal  termination  of  the  bile-duct  and  canal  of  Wir- 
sung (papilla  Vateri)  (Fig.  193).  The  duct  of  Santorini  usually 
tapers  toward  the  duodenal  opening  from  its  point  of  departure 
from  the  main  duct,  its  caliber  gradually  diminishing  in  the  di- 
rection indicated,  so  that  it  is  smaller  at  the  duodenal  opening 
than  at  the  point  of  confluence  with  the  main  duct  (Fig.  189). 
Hence  the  secretion  from  the  proximal  head  portion  of  the  pan- 
creas, conveyed  by  this  duct  and  its  tributaries,  passes  usually  into 
the  main  pancreatic  duct  and  not  directly  into  the  intestine 
through  the  duodenal  opening  of  the  duct  of  Santorini.  The 
latter  is,  however,  thus  enabled  to  vicariously  take  upon  itself 
the  conduct  of  the  pancreatic  secretion  in  cases  of  obstruction  or 
obliteration  of  the  main  duct  (calculi,  ulcers,  cicatrices,  etc.).  In 
these  cases  of  obstruction  of  the  main  duct  the  duct  of  Santorini 
enlarges  and  performs  its  functions. 

8 


114  ANATOMY  OF  THE  PERITONEUM, 

Occasionally,  without  obstruction  of  the  main  duct,  the  duo- 
denal opening  of  the  duct  of  Santorini  is  large,  and  the  flow  of 
secretion  evidently  the  reverse  of  the  usual,  i.  e.,  directly  into 
the  intestine. 

In  other  cases,  also  without  pathological  conditions,  the  prox- 
imal duct  is  the  larger  of  the  two  and  serves  as  the  principal 
channel  of  pancreatic  secretion,  the  canal  of  Wirsung  being  small. 
This  is  evidently  a  persistence  and  further  development  of  the 
early  embryonic  relative  condition  of  the  two  outgrowths  above 
described  (Fig.  190).  On  the  other  hand  the  duct  of  Santorini 
may  not  open  at  all  into  the  duodenum,  terminating  in  small 
branches  which  drain  the  proximal  part  of  the  head  of  the  gland 
Fig.  191). 

Schirmer  has  examined  the  arrangement  of  the  pancreatic  ducts 
in  105  specimens.  In  56  of  these  the  duct  of  Santorini  passed 
from  the  main  duct  into  the  duodenum,  opening  upon  a  papilla 
situated  2.5  cm.  above  the  common  opening  of  the  bile  duct  and 
canal  of  Wirsung. 

In  19  the  duct  of  Santorini  was  well  developed  but  did  not 
open  into  the  duodenum. 

In  but  4  cases  the  duct  of  Santorini  formed  the  only  pancreatic 
duct,  the  lower  opening  being  occupied  by  the  bile  duct  alone 
(Fig.  192).  We  may  assume  in  these  cases  failure  of  develop- 
ment of  the  distal  outgrowth  connected  with  the  primitive  hepatic 
bud,  leaving  only  the  proximal  duodenal  outgrowth  to  form  the 
entire  adult  gland. 

Figs.  188  and  189  show  the  normal  arrangement  of  the  duo- 
denal openings  of  the  biliary  and  pancreatic  ducts. 

Figs.  190  to  192  show  schematically  the  variations  in  the  rela- 
tive development  and  the  adult  arrangement  of  the  pancreatic 

ducts. 

Diverticulum  and  Papilla  Vateri — From  what  has  been  said  re- 
garding the  embryonic  union  of  the  distal  pancreatic  outgrowth 
with  the  hepatic  bud  it  will  be  easy  to  recognize  the  corresponding 
features  in  the  arrangement  of  the  adult  duodenal  termination  of 


DEVELOPMENT  OF  PANCREAS  IN  LOWER    VERTEBRATES.       115 

the  common  bile-duct  and  canal  of  Wirsung.  The  dilated  interior 
of  the  duodenal  papilla  (diverticulum  Vateri)  corresponds  to  the 
embryonic  segment  between  the  intestinal  opening  of  the  primi- 
tive liver  duct  and  the  point  when  this  duct  gives  off  the  distal 
larger  pancreatic  outbud  (Figs.  186,  187,  188,  193  and  194). 

The  union  of  the  pancreatic  and  biliary  ducts  to  form  the  recess 
of  the  diverticulum  Vateri,  which  then  opens  by  a  single  common 
orifice  into  the  duodenum,  is  better  marked  in  some  of  the  lower 
vertebrates  than  in  man. 

Fig.  195  shows  the  proximal  portion  of  the  duodenum  of  the 
cassowary  (Casuarius  casuarius)  with  the  biliary  and  pancreatic 
ducts  and  the  diverticulum  at  their  confluence  in  section. 

The  development  of  these  two  main  digestive  glands  as  diver- 
ticula from  the  intestinal  canal  also  explains  the  direct  continuity 
of  the  mucous  membrane  of  their  ducts  with  that  lining  the  duo- 
denum, a  fact  which  is  of  considerable  importance  in  the  patho- 
logical extension  of  mucous  inflammations  from  the  intestine  to 
the  duct  system  of  the  glands. 

Development  of  the  Pancreas  in  Lower  Vertebrates. — In  the  em- 
bryo of  the  sheep  two  pancreatic  buds  are  found,  but  the  duct  of 
the  dorsal  (proximal)  outgrowth  (duct  of  Santorini)  subsequently 
fuses  entirely  with  the  main  duct. 

In  the  cat  there  are  likewise  two  pancreatic  outgrowths. 

In  the  chick  three  pancreatic  buds  are  visible  about  the  fourth 
day. 

Amphibia  likewise  present  three  embryonic  pancreas  buds. 

The  ventral  (distal)  outgrowth  is  double,  the  two  portions  pro- 
ceeding symmetically  from  each  side  of  the  hepatic  duct.  The 
single  dorsal  outgrowth  is  derived  directly  from  the  duodenal 
epithelium.  Later  on  all  these  outgrowths  fuse  to  form  the  single 
adult  gland. 

Fish  also  possess  several  (up  to  four)  embryonic  pancreatic  out- 
growths. 

Recently  in  human  embryos  of  4.9  mm.  cervico-coccygeal  meas- 
ure three  pancreatic  outgrowths  have  been  observed,  all  entirely 


116  ANATOMY  OF   THE  PERITONEUM. 

distinct  from  each  other,  one  dorsal,  budding  from  the  epithelium 
of  the  primitive  duodenum  and  two  ventral,  proceeding  from  the 
grooved  gutter  which  represents  the  primitive  ductus  choledochus 
at  this  period.  In  embryos  of  from  6  to  10  mm.  the  two  ventral 
outgrowths  have  already  fused,  hence  only  two  buds,  a  single 
ventral  and  a  dorsal,  are  now  encountered.^ 

These  observations  place  the  development  of  the  human  pan- 
creas in  line  with  the  triple  pancreatic  outgrowths,  two  ventral 
and  one  dorsal  characteristic  of  the  majority  of  the  lower  verte- 
brates, which  have  been  hitherto  carefully  examined.  The  ven- 
tral or  distal  bud  is  probably  double  in  the  majorit}''  of  vertebrates. 
The  two  segments  fuse,  however,  so  early  that  the  derivation  of 
the  pancreas  from  a  double  outgrowth,  as  described  above  for  the 
human  embryo,  practically  obtains.  In  forms  in  which  the 
adult  gland  presents  a  number  of  separate  openings  into  the  duo- 
denum (cf  p.  118),  the  development  would  probably  show  mul- 
tiple embryonic  outgrowths  from  the  intestinal  hypoblast. 

In  any  case  the  dorsal  pancreatic  bud  appears  to  have  developed 
in  the  vertebrate  series  before  the  ventral  outgrowth  and  to  be 
hence  phylogenetically  the  older  structure. 

COMPARATIVE  ANATOMY  OF  THE  PANCREAS. 

With  the  exception  of  Amphioxus  and  probably  also  of  the 
Cyclostomata,  the  gland  appears  to  be  present  in  all  vertebrates, 
varying,  however,  much  in  size,  shape  and  relation  to  the  intes- 
tinal tube.  Usually  it  appears  as  an  elongated,  flattened,  more  or 
less  distinctly  lobulated  organ,  in  close  apposition  to  the  duo- 
denum between  the  layers  of  the  mesoduodenum.  In  all  forms 
in  which  the  gland  is  found  it  is  connected  with  the  post-gastric 
intestine  and  marks  the  beginning  of  the  midgut.  In  structure 
the  gland  is  usually  acinous,  resembling  the  salivary  glands.  It 
is  well  developed  in  the  selachians,  forming  a  triangular  body 
connected  with  the  beginning  of  the  midgut  (Fig.  202).  In 
some  instances  the  gland  elements  do  not  extend  beyond  the  in- 

'  lankelowitz,  Arch.  f.  Mikr.  Anat.,  Bd.  46,  1895. 


COMPARATIVE  ANATOMY  OF  THE  PANCREAS.  117 

testine  itself,  but  remain  imbedded  in  the  wall  of  the  midgut,  as 
in  Protopterus.  In  certain  adult  teleosts  the  pancreas  is  sur- 
rounded by  the  liver  (Fig.  196),  in  others  it  does  not  appear  as  a 
compact  gland  but  is  distributed  in  the  form  of  finely  scattered 
lobules  throughout  the  mesentery  between  the  two  layers  of  this 
membrane.  On  account  of  this  concealed  position  of  the  gland 
it  was  formerly  believed  that  the  adult  teleosts  did  not  possess  a 
pancreas.  The  pyloric  caeca  (cf  p.  119)  found  in  these  forms  were 
consequently  considered  to  be  homologous  with  the  pancreas  of 
the  higher  vertebrates. 

In  Myxinoids  a  peculiar  lobulated  glandular  organ  is  found 
imbedded  in  the  peritoneal  coat  of  the  intestine  near  the  entrance 
of  the  bile-duct,  into  which  its  lobules  open  separately.  This 
organ  possibly  corresponds  to  the  higher  vertebrate  pancreas. 

An  organ  which  may  represent  a  dorsal  pancreas  is  also  devel- 
oped in  Ammocostes  (larva  of  Petromyzon),  but  its  exact  homol- 
ogy is  still  doubtful.  It  is  possible  that  a  true  pancreas  has 
not  yet  developed  in  the  cyclostomata.  In  Amphioxus  no  trace 
of  a  pancreas  is  found.  In  all  other  vertebrates  the  gland  is 
present.  In  certain  amphibians,  as  the  frog,  the  single  pancreatic 
duct  opens  into  the  common  bile  duct  (Fig.  197). 

In  lacertilians  and  in  some  chelonians  a  lateral  offshoot  of  the 
pancreas  is  directed  transversely  and  is  adherent  to  the  spleen. 
Fig.  113  shows  the  gland  in  Chelydra  serpentaria.  While  the 
gland  usually  has  a  single  duct,  yet  two  ducts  are  found  in  a 
number  of  animals  (many  mammals,  birds,  chelonians  and 
crocodiles).  At  times  three  ducts  are  encountered,  as  in  the 
chicken  and  pigeon. 

The  arrangement  of  the  pancreatic  duct  system  among  mam- 
malia presents  the  following  variations : 

1.  Mammals  with  one  pancreatic  duct,  either  connected  with 
the  bile-duct  or  entering  the  intestine  independently : 

Monkeys,  most  rodents  (except  the  beaver),  marsupials,  car- 
nivora  (except  dog  and  hyena),  many  ungulates  (pig,  peccary, 
hyrax,  etc.),  most  ruminating  artiodactyla. 


118  ANATOMY  OF  THE  PERITONEUM. 

(a)  The  pancreatic  duct  joins  the  common  bile-duct  before  en- 
tering the  duodenum  in  the  monkeys,  marsupials,  carnivora,  in  the 
sheep,  goat  and  camel. 

The  point  of  entrance  of  the  combined  duct  into  the  intestine 
varies.  In  some  forms  it  is  near  the  pylorus,  in  others  at  some 
distance  from  the  same.  The  common  opening  is  situated  li"  to 
2"  beyond  the  pylorus  in  carnivora,  and  one  foot  behind  the  same 
point  in  the  goat  and  sheep. 

(6)  The  pancreatic  duct  does  not  join  the  bile-duct,  but  empties 
separately  into  the  intestine,  in  most  rodents  and  in  the  calf  and  pig. 

In  the  calf  the  pancreatic  duct  opens  into  the  duodenum  15' 
beyond  the  bile-duct  and  3'  beyond  the  pylorus. 

In  the  pig  the  pancreatic  opening  is  5"-7"  beyond  that  of  the 
bile-duct  and  6"-8"  behind  the  pylorus. 

2.  Mammals  with  two  pancreatic  ducts,  of  which  one  usually 
joins  the  bile-duct :  perissodactyla  (except  the  ass  according  to 
Meckel),  elephant,  beaver,  several  carnivora,  dog,  hyena,  and 
according  to  Bernard  the  cat.  In  the  perissodactyla  the  prox- 
imal of  the  two  pancreatic  ducts  empties,  either  combined  mth 
the  bile-duct,  or  separate  from  it,  but  very  close  to  it,  3"-4"  be- 
hind the  pylorus.  The  second  distal  duct  is  smaller  and  opens 
several  inches  further  down. 

In  most  rodents  the  pancreatic  entrance  is  placed  at  some  dis- 
tance from  the  pylorus.  Fig.  199  shows  the  arrangement  of  the 
parts  in  the  rabbit,  in  which  animal  the  main  distal  pancreatic 
duct  empties  at  a  distance  of  13"-14"  from  the  pylorus  into  the 
end  of  the  duodenum,  which  intestine  forms  a  very  long  loop, 
while  the  biliary  duct,  receiving  the  smaller  proximal  pancreatic 
duct,  opens  near  the  pylorus. 

In  the  beaver  the  smaller  proximal  duct  joins  the  bile-duct  or 
even  enters  the  duodenum  anterior  to  the  bile-duct,  nearer  the 
pylorus,  while  the  distal  larger  pancreatic  duct  opens  into  the  in- 
testine 16"-18"  behind  the  biliary  duct.  Of  the  two  ducts  found 
in  the  dog  (Fig.  200)  the  smaller  proximal  either  joins  the  bile- 
duct  or  opens  into  the  intestine  close  to  it,  T'-li"  beyond  the 


PYLORIC  CJECA  OR  APPENDICES.  119 

pylorus.  The  larger  distal  duct  opens  into  the  duodenum  V'-lh" 
behind  the  bihary  duct.  Fig.  201  shows  the  dog's  stomach  and 
proximal  portion  of  the  duodenum  in  section.  The  proximal 
smaller  pancreatic  duct  here  joins  the  biliary  duct,  and  opens  with 
it  by  a  single  orifice  into  the  duodenum.  The  distal  larger  pan- 
creatic duct  opens  independently  into  the  intestine  further  caudad. 

The  parts  in  Hysena  present  a  similar  arrangement. 

Bernard  always  found  two  pancreatic  ducts  in  the  cat,  one  large 
principal  duct  and  a  second  smaller  accessory  duct.  Of  these,  the 
one  situated  nearest  to  the  pylorus  always  united  with  the  bile- 
duct.  The  pancreatic  duct  thus  joining  the  bile-duct  was  some- 
times the  main  duct,  sometimes  the  accessory  smaller  duct. 

Since  the  main  function  of  the  pancreatic  juice  is  the  conver- 
sion of  starch  into  sugar,  the  gland  appears  better  developed  in 
general  in  herbivora  than  in  carnivora,  without,  however,  disap- 
pearing in  the  latter.  In  fact  it  is  of  considerable  size  in  the 
carnivora,  because  the  secretion  also  acts  on  the  albuminous  food 
substances  and,  though  to  a  lesser  degree,  on  the  fats. 

PYLORIC   GMGA  OR  APPENDICES. 

In  the  Cyclostomata  and  Selachians  the  intestinal  canal  is  in  the 
main  free  from  csecal  appendages,  while  a  large  portion  of  the 
tube  is  provided  with  a  special  fold  of  the  mucous  membrane 
which  projects  into  the  lumen  of  the  gut  (spiral  valve).  Fig.  43 
shows  the  straight  intestinal  tract  with  the  spiral  valve  of  the 
longer  distal  segment  in  a  cyclostome,  Petromyzon  marinus  or 
lamprey.  In  Figs.  202  and  203  the  selachian  (shark)  intestine  is 
represented  in  two  examples,  while  the  similar  spiral  valve  in  a 
Dipnoean  or  lung  fish,  Ceratodus,  is  seen  in  Fig.  204. 

On  the  other  hand  in  the  Ganoids  and  in  many  Teleosts  longer 
or  shorter  finger-shaped  diverticula  of  the  midgut  are  found  im- 
mediately bej^ond  the  pylorus  in  the  region  of  the  bile-duct. 

These  pouches  or  diverticula  of  the  intestine  form  the  so-called 
pyloric  caeca  or  appendices  of  these  fish.  They  vary  very  much 
in  length,  diameter  and  number  in  different  forms. 


120  ANATOMY  OF  THE  PERITONEUM. 

Thus  but  a  single  diverticulum  appears  in  Folypterus  and  Ammo- 
dytes  (Fig.  205).  Rhombus  maximus  and  Echelus  conger(Figs.  112  and 
206)  have  two,  and  the  same  number  appear  in  Lophius  piscatorius 
(Fig.  207).  Perca  has  three  and  the  Pleuronedidxhsiye  three  to  five. 

Fig.  208  shows  the  stomach  and  the  beginning  of  the  midgut 
with  four  pyloric  caeca  in  Pleuronectes  maculatus,  and  Fig.  209 
the  same  parts  of  this  animal  in  section. 

Fig.  210  shows  the  stomach  and  midgut  of  Paralichthys  dentatus, 
the  summer  flounder,  with  three  well-developed  conical  pyloric 
caeca.  On  the  other  hand  in  some  forms  the  number  of  pyloric 
appendices  is  enormously  increased,  while  their  caliber  dimin- 
ishes. Thus  191  csecal  appendages  are  found  surrounding  the 
beginning  of  the  midgut  in  Scomber  scomber.  A  well-marked 
example  of  prolific  development  of  the  pyloric  appendages  is 
furnished  by  the  common  cod,  Gadus  callarias  (Fig.  211).  The 
appendices  are  in  the  natural  condition  bound  together  by  connec- 
tive tissue  and  blood  vessels,  so  as  to  form  a  compact  organ,  re- 
sembling a  gland  (Fig.  21 1,  A),  and  a  similar  arrangement  is  found 
in  Thynnus  vulgaris  and  alalonga,  Pelamys  and  Accipenser  (Fig.  212). 

In  some  Teleosts  (Siluroidea,  Labroidea,  Cyprinodontia,  Plecto- 
gnathi  and  Leptobranchiates)  the  appendices  are  entirely  wanting. 
If  there  are  not  more  than  8-10  appendices  they  usually  surround 
the  gut  and  empty  into  the  same  in  a  circle.  In  other  cases  they 
are  arranged  in  a  single  line,  or  in  a  double  row,  opposite  to  each 
other  (Fig.  213).  Each  appendix  may  open  into  the  intestine 
independently,  this  especially  where  the  number  is  limited  and 
the  individual  pouches  large  (cf  Figs.  206-210),  or  several  may 
unite  to  form  a  common  duct. 

Fig.  211,  B,  shows  the  appendices  in  Gadus  callarias,  the  cod, 
freed  by  dissection  from  the  investing  connective  and  vascular 
tissue.  It  will  be  noticed  that  a  considerable  number  of  the  tubes 
unite  to  form  ducts  of  larger  caliber  which  open  into  the  intestine, 
as  seen  in  the  section  shown  in  Fig.  214. 

The  pyloric  appendices  apparently  have  the  same  significance  as 
the  spiral  intestinal  fold  of  the  Selachians,  Cyclostomes  and  Dip- 


PLATE    CV. 


VENTRAL 

MESOGAS- 

TRIUM 


DUODENUM 


DORSAL    MESO- 
GASTRIUM   FORM- 
ING   OMENTAL 
POUCH 

STOMACH 


CEPHALIC    PRO- 
TON OF  PANCREAS 

MESODUOOENUM 
CAUDAL  PROTON 
OF    PANCREAS 


Fig.  215.— Cephalic  segment  of  primitive  mesentery  in  sclicmatic  profile  view. 


VENTRAL  MESO 
GASTHIUM 


DUODENUM 


DORSAL    MESO- 
GASTRIUM 


DISTAL     PORTION     OF 
PANCREAS,         DEVEL- 
OPING     BETWEEN 
LAYERS    OF      DORSAL 
MESOGASTRIUM 


MARGIN    OF 
OMENTAL  BURSA 


MESOOUODENUM 

PROXIMAL    PORTION 
(head)  OF  PANCREAS 
DEVELOPING    BE- 
TWEEN     LAYERS 
OF  MESODUOO- 
ENUM 


Fig.  216.— Schematic  profile  view  of  i)rimitive  mesenteries  with  formation  of  omental 
Dursa  and  developing  spleen  and  pancreas. 


PLATE    CVI. 


CESOPHAGUS 


DUODENUM 


STOMACH 
OMENTAL  BURSA 
SPLEEN 

PANCREAS 

DUODENO- 
JEJUNAL 
FLEXURE 


MESENTERY    OF 
SMALL  INTESTINE 


Fig.  217.— Sos  scrofa  fmt.,  foetal  pig.     Portions  of  tlioracic  and  abdominal  viscera  hardened  in 
situ.     (Columbia  University  Museum,  No.  1449.) 


DORSAL  MESOGAS- 
TRIUM  FORMING 
OMENTAL   BURSA 

STOMACH 


DUODENUM 


ILEO-COLIC 
JUNCTION 
PRIMITIVE   DOR- 
SAL   MESEN- 
TERY OF  INTES- 
TINAL    LOOP 
FORMING   MESEN- 
TERY OF  SMALL 
INTESTINE    AND 
ASCENDING    MESO- 
COLON 


SMALL  INTESTINE 


MESODUODENUM 
TRANSVERSE    COLON 

SPLENIC    FLEXURE 

INFRACOLIC  SEGMENT 
OF    DUODENUM 


DESCENDING    COLON 


PRIMITIVE    DORSAL 
MESENTERY    FORMING 
OESC     MESOCOLON 


i 


Fig.  218.— Schematic  view  of  primitive  mesentery  after  intestinal  rotation  and  incipient 
formation  of  omental  bursa  from  dorsal  mesogastrium. 


PLATE    CVII. 


STOMACH 

GASTRO-SPLENIC 

OMENTUM 


PANCREAS 


AORTA    GIVING 
OFF    SPLENIC 
ARTERY 


Figs.  219,  220. — Schematic  transection  of  dorsal  mesogastrium,  pancreas,  spleen,  and  stomach. 
Fig.  219. — Before  adhesion  to  primitive  parietal  peritoneum  (arrow  indicates  the  direction  in 
which  the  adhesion  takes  place). 


GASTRO-SPLENIC    OMENTUM 

CONTAINING  A.  GASTRO-EPI- 

PLOICA   SINISTRA 

SPLEEN 
PANCREAS 

SECONDARY  LINE  OF  TRANS- 
ITION    BETW.     VISCERAL    AND 

parietal    peritoneum 

s.     lieno-renale,     lig. 

lieno-phrenicum) 

L     KIDNEY 


AREA  OF  ADHESION  BETWEEN  PRIMITIVE 
PARIETAL  PERITONEUM  AND  DORSAL  MESO- 
GASTRIUM, CARRYING  SPLENIC  ART.  AND  IN- 
VESTING   DORSAL    SURFACE    OF    PANCREAS 


Fig.  220. — After  adhesion  and  formation  of  secondary  line  of  transition  between  mesogastrium 
and  parietal  peritoneum  (lieno-reiiiil  ligament). 


PLATE   CVIIl. 


PANCREAS 


GREAT 
OMENTUM 


DORSAL  MCSO- 
GASTRIUM 


PARIETAL 
PERITONEUM 


Figs.  221,  222. — Schematic  sagittal  sections  through  stomach,  pancreas,  great  omentum,  and 
left  kidney. 

Fig.  221. — Before  adhesion  between  dorsal  and  mesogastrium  and  parietal  peritoneum. 


AREA     OF     ADHESION 
BETWEEN       PARIETAL 
PERITONEUM      AND 
DORSAL    MESOGAS- 
TRIUM 


Fig.  222.— After  adhesion. 


PLATE   CIX. 


CESOPHAGUS 


STOMACH 


SPLEEN 
GASTRIC    ARTERY 


CCELIAC    AXIS 

SPLENIC    ART 
BODY  AND  TAIL  OF  PAN 

CREAS  INCLUDED  IH.  ^^ 
DORSAL  MESOGASTRIUM~Tf; 
SUP     MESENTERIC  ART 


LINE  OF   ATTACHMENT 

OF    DORSAL    MESO-' 

GASTRIUM 


POSTCAVA 
SI^TGELIAN    LOBE 
PORTAL   VEIN 
HEPATIC   ARTERY 

-^GALL-BLADDER 


DUODENUM 

HEAD  OF  PANCREAS, 
INCLUDED  IN  MESO- 
DUODENUM 


Fig.  223. — Abdominal  viscera  of  cat,  hardened  and  removed  from  body,  showing  relation  of 
pancreas  to  mesoduodenum  and  dorsal  mesogastrium,  respectively.  (Columbia  University 
Museum,  No.  728.) 


DIAPHRAGM 


GASTRO-HEPATIC 
OMENTUM 

STOMACH 


PANCREAS 

DUODENUM 
TRANSV . COLON 


JEJUNO-ILEUM 


Fig.  224.— Schematic  sagittal  section  of  abdominal  viscera  of  cat,  after  the 
intestines  have  been  rotated  to  correspond  to  the  adult  human  disposition,  to  show- 
lines  of  peritoneal  reflection  before  adhesion. 


PLATE    ex. 


DIAPHRAGM 


GASTRO-HEPATIC 
OMENTUM 
STOMACH 

PANCREAS 

DUODENUM 

TRANSVERSE 
COLON 


SMALL 
INTESTINE 


Fig.  225. — The  same  figure  indicating  the  areas  of  adhesion  and  peri- 
toneal obliteration  (shaded)  which  produce  the  arrangement  of  the  adult 
human  peritoneum. 

1.  Area  of  adhesion  between  opposed  surfaces  of  great  omentum  and  trans- 
verse mesocolon  and  colon. 

2.  Area  of  adhesion  between  parietal  peritoneum,  duodenum,  and  caudal 
layer  of  transverse  mesocolon. 

3.  Adhesion  of  opposed  walls  of  omental  bursa  leading  to  obliteration  of 
distal  portion  of  pouch  and  producing  "  gastro-colic  "  ligament  of  adult  human 
subject. 


PANCREAS 

CAUDAL    LAYER 
TRANSV.    MESOCOLON 
DUODENUM 

TRANSV.    COLON 
MESENTERY 
SMALL  INTESTINE 


1  2 

Fig.  226. — Schematic  sagittal  section  of  adult  human  peritoneum. 


i 


PLATE    CXI. 


GREAT  OMENTUM' 


VENTRAL  BORDER  OF 
PANCREAS,  WITH  AT- 
TACHMENT OF  RE- 
CURRENT LAYERS  OF 
GREAT   OMENTUM 


ASC.   MESOCOLON 
SUP.  MESENTERIC  A. 


ASC.    COLON 

TRANSV.   COLON 

CUT  EDGE  OF  MESE 

SMALL  INTESTINE  C 

OUS  WITH  ASC.   MESOCOLON 

ILEO-COLIC 

JUNCTION 


NTERY   OF_    ^^s •^'•lA 

CONTINU-     ''^r~    "^'A* 


LEFT   LOBE   OF   LIVER 


STOMACH 


PANCREAS,  CAUDAL  SURFACE 
CUT  END  OF  DUODENUM 

L.  KIDNEY     BEHIND  PRIMARY 
PARIETAL    PERITONEUM 

CEPHALIC  LAYER 
OF  TRANSVERSE 
MESOCOLON 


DESCENDING 
MESOCOLON 


OMEGA    LOOP 


r-crr.  ^^^"   ^?J,-T'^¥.""H"^^  ^^^■^*^'  °^  Macacus  rhesus,  Rhesus  moukey,  with  the  small  intestine 
removed.     (Columbia  University  Museum,  No.  tHt-) 


PLATE    CXIl. 


DIAPHRAGM 


STOMACH 


PANCREAS 


DORSAL 
MESOGASTRIUM 


Figs.  228-232. — Scheniatic  sagittal  sections  of  dorsal  mesugas- 
tritim  and  omental  bur.sa,  in  man,  monkey,  and  cat. 

Fig.  228. — Common  embryonal  condition,  as  illustrated  by  cat,  after 
rotation  and  formation  of  omental  bursa. 


STOMACH 


PANCREAS 


KIDNEY 

AREA    OF    ADHESION 
BETWEEN       DORSAL 
MESOGASTRIUM    AND 
PRIMITIVE     PARIETAL 
PERITONEUM 


Fig.  229. — Area  of  adhesion  between  dorsal  mesogastriiim  and  jirimitive 
parietal  peritoneum  in  Macacus,  producing  condition  shown  in  Fig.  230. 


PYLORIC  GjECA   or  APPENDICES.  121 

noeans,  i.  e.,  the  production  of  an  increase  in  the  area  of  the  diges- 
tive and  absorbing  surfaces  of  the  intestinal  mucous  membrane. 
Hence,  as  stated,  the  appendices  and  the  spiral  fold  are  found  to 
vary  in  inverse  ratio  to  each  other.  Thus,  for  example,  Polyp- 
terus  (Fig.  205)  still  has  a  fairly  well  developed  spiral  fold  and 
only  a  single  pyloric  appendix,  while  Lepidosteus,  with  but  slightly 
developed  spiral  fold,  has  numerous  appendices.  It  was  formerly 
held  that  the  pyloric  caeca  and  the  pancreas  were  mutually  in- 
compatible structures,  and  that  where  one  is  found  the  other  will 
be  wanting. 

Hence  the  appendices  were  regarded  as  homologous  with  the 
pancreas  of  the  higher  forms.  Recent  observations  have  shown 
that  this  view  is  not  strictly  and  entirely  correct,  while  at  the 
same  time  it  merits  consideration  in  several  respects. 

It  is  true  that  the  pancreas  in  certain  teleosts  is  now  known  to 
be  present  although  concealed  from  observation  in  the  liver  or 
scattered  in  the  form  of  small  lobules  between  the  layers  of  the 
mesentery  (cf  p.  117),  and  that  in  a  number  of  fish,  such  as  Salmo 
salar,  Clupea  harengus,  Accipenser  sturio,  both  the  appendices  and 
the  pancreas  are  encountered.  Consequently  these  structures 
are  not  identical  or  even  completely  homologous,  since  they  occur 
side  by  side  in  the  same  form. 

On  the  other  hand  Krukenberg  has  demonstrated  that  the  ap- 
pendices pyloricae  may  function  physiologically  as  a  pancreas  by 
yielding  a  secretion  which  corresponds  to  the  pancreatic  juice  in 
its  digestive  action.  In  the  majority  of  forms,  however,  they  ap- 
parently merely  increase  the  intestinal  absorbing  surface,  secret- 
ing only  mucus. 

These  structures  are  nevertheless  very  interesting  and  instruc- 
tive since  they  furnish  a  perfect  gross  morphological  illustration 
of  the  embryonal  stages  just  considered  in  connection  with  the 
development  of  the  mammalian  pancreas.  In  the  adult  ganoid 
or  teleost  these  blind  diverticula  or  pouches,  varying  greatly  in 
.shape,  number  and  size,  protrude  from  the  intestine  immediately 
beyond  the  pylorus,  usually  in  close  connection  with  the  duo- 


122  ANATOMY  OF  THE  PERITONEUM. 

denal  entrance  of  the  bile-duct.  Two  or  more  of  these  pouches 
may  unite  to  form  a  common  duct  or  canal  opening  into  the 
intestine. 

These  forms,  therefore,  offer  direct  and  valuable  morphological 
illustration  of  the  manner  in  which  the  pancreas  of  the  higher 
vertebrates  develops,  i.  e.,  as  a  set  of  hollow  outgrowths  or 
diverticula  from  the  hypoblast  of  the  primitive  enteric  tube. 
We  can  establish  a  consecutive  series,  beginning  with  forms  in 
which  only  one  or  two  diverticula  are  found,  and  extending  to 
types  in  which  the  number  of  the  little  cylindrical  pouches 
reaches  nearly  two  hundred  and  in  which  they  are  bound  to- 
gether by  connective  tissue  and  blood  vessels  so  as  to  closely 
resemble  the  structure  of  a  glandular  pancreas.  This  is  one  of 
the  most  striking  instances  in  which  the  minute  embryological 
stages  of  the  higher  types  are  directly  illustrated  by  the  permanent 
adult  conditions  found  in  the  lower  vertebrates.  [The  same 
statement,  as  we  will  see,  holds  good  in  reference  to  the  develop- 
ment of  the  liver.'] 

RELATION  OF  THE  PANCREAS  TO  THE  PERITONEUM. 

The  gland  becomes  very  intimately  connected  with  the  serous 
layers  of  the  primitive  dorsal  mesentery.  In  order  to  clearly 
comprehend  the  adult  serous  relations  it  is  necessary  to  make  a 
distinction  between  two  divisions  or  portions  of  the  gland,  based 
upon  the  altered  relations  of  the  primitive  dorsal  mesentery 
which  result  from  the  differentiation  of  the  primitive  simple 
intestinal  tube  into  stomach  and  duodenum. 

1.  The  primary  outgrowth  of  the  pancreatic  tubules  from  the 
duodenum,  i.  e.,  the  part  which  is  to  form  the  "head"  of  the 
adult  gland,  is  situated  between  the  two  layers  of  that  division 
of  the  primitive  dorsal  mesentery  which  forms,  after  differen- 
tiation of  stomach  and  small  intestine,  the  mesoduodenum. 
Coincident  with  the  rotation  of  the  stomach,  as  we  have  seen, 
the  duodenum  and  mesoduodenum  exchange  their  original  sag- 
ittal position  in  the  median  plane  of  the  body  for  one  to  the  right 


RELATION  OF  THE  PANCREAS  TO  THE  PERITONEUM.  123 

of  the  median  line,  balancing,  so  to  speak,  the  extension  of  the 
stomach  to  the  left  (Fig.  218). 

The  original  right  layer  of  the  mesoduodenum  and  the  right 
surface  of  the  duodenum  now  look  dorsad  and  rest  in  contact 
with  the  parietal  peritoneum  investing  the  right  abdominal  back- 
ground and  the  ventral  surface  of  the  right  kidney  and  inferior 
vena  cava.  We  have  already  seen  that  the  descending  portion  of 
the  duodenum  in  man  becomes  anchored  in  this  position  by  ad- 
hesion of  these  apposed  peritoneal  surfaces.  This  fixation  in- 
cludes, of  course,  the  structures  situated  between  the  layers  of  the 
mesoduodenum,  i,  e.,  the  head  of  the  pancreas.  Consequently, 
after  rotation  and  adhesion,  this  portion  of  the  gland  turns  one 
surface  ventrad,  invested  by  secondary  parietal  peritoneum,  origi- 
nally the  left  leaf  of  the  free  mesoduodenum,  while  the  original 
right  surface  of  the  gland  has  become  the  dorsal  and  has  lost  its 
mesoduodenal  investment  by  adhesion  to  the  primary  parietal 
peritoneum. 

2.  In  order  to  understand  the  way  in  which  the  body  and  tail 
of  the  pancreas  obtain  their  final  peritoneal  relations  it  is  neces- 
sary to  consider  the  development  of  the  doi«al  mesogastrium  to 
form  the  omental  bag.  If  we  regard  the  primitive  dorsal  mesen- 
tery in  the  profile  view  from  the  left  side  (Fig.  215)  it  will  be  seen 
that,  as  already  stated,  the  mesoduodenum  is  the  first  part  of  the 
membrane  to  be  invaded  by  the  pancreatic  outgrowth  from  the 
intestine.  Cephalad  of  the  mesoduodenum  the  primitive  dorsal 
mesogastrium  (Fig.  215)  is  seen  to  protrude  to  the  left  and  cau- 
dad  to  form,  as  already  explained,  the  cavity  of  the  omental 
bursa  of  the  retrogastric  space  ("lesser  peritoneal  sac").  The 
further  growth  of  the  pancreas  carries  the  developing  gland  from 
the  district  of  the  mesoduodenum  into  that  portion  of  the  dorsal 
mesogastrium  which  now  forms  the  dorsal  wall  of  the  omental 
bursa  (Fig.  216). 

This  double  relation  of  the  pancreas  to  the  mesoduodenum  and 
to  the  mesogastrium  forming  the  omental  bursa  is  well  seen  in 
foetal  pigs  between  two  and  three  inches  in  length  (Fig.  217). 


124  ANATOMY  OF  THE  PERITONEUM. 

The  head  portion  of  the  pancreas  is  seen  developing  between 
the  layers  of  the  mesoduodenum,  while  the  body  and  tail  of  the 
gland,  extending  to  the  left,  grows  between  the  two  dorsal  layers 
of  the  omentum  bursa  towards  the  spleen,  which  organ  is  found 
connected  with  the  left  and  dorsal  extremity  of  the  omental  sac 
derived  from  the  dorsal  mesogastrium. 

Before  the  growth  of  the  great  omentum  is  pronounced  the 
continuity  of  the  mesoduodenum  and  dorsal  mesogastrium  can 
be  readily  appreciated  (Fig.  218).  But  after  the  redundant 
growth  of  the  membrane  has  carried  the  great  omentum  further 
caudad,  the  stomach  and  the  two  omental  layers  attached  to 
the  greater  curvature  lie  in  front  of  the  structures  included 
between  the  two  dorsal  layers  and  conceal  them  from  view  (Fig. 
177). 

In  sagittal  sections  to  the  left  of  the  median  line  (Figs.  221  and 
222)  the  pancreas  now  appears  included  between  the  layers  of  the 
great  omentum  near  their  point  of  departure  from  the  vertebral 
column.  (This  point  is  of  course  identical  with  the  prevertebral 
attachment  of  the  primitive  dorsal  mesogastrium  from  which  the 
omentum  is  developed.) 

The  foregoing  considerations  will,  therefore,  lead  to  the  conclu- 
sion that  the  pancreas  presents,  in  regard  to  its  peritoneal  rela- 
tions, two  distinct  segments  : 

1.  The  portion  adjacent  to  duodenum  (head  and  neck  of 
the  gland)  is  developed  between  the  layers  of  the  mesoduode- 
num. 

2.  The  distal  portion  of  the  gland,  comprising  the  body  and 
tail,  develops  between  the  layers  of  the  great  omentum  (dorsal 
segment),  derived  from  the  primitive  dorsal  mesogastrium. 

The  transections  of  the  dorsal  mesogastrium  shown  in  Figs. 
180  and  181  will  now  have  to  be  amplified  by  the  introduction  of 
the  body  of  the  pancreas  between  the  two  layers  of  the  vertebro- 
splenic  segment,  in  addition  to  the  splenic  artery  (Figs.  219  and 
220). 

Hence  the  following  facts  will  be  understood : 


RELATION  OF  THE  PANCREAS  TO  THE  PERITONEUM.  125 

1.  In  the  adult  the  splenic  artery  supplies  a  series  of  small 
branches  to  the  pancreas  as  it  courses  along  the  cephalic  border  of 
the  gland  on  its  way  to  the  spleen. 

2.  After  the  above-described  adhesion  of  the  original:  left  leaf 
of  the  dorsal  mesogastrium  (vertebro-splenic  segment)  to  the 
parietal  peritoneum  (Fig.  220),  the  dorsal  surface  of  the  body 
of  the  pancreas  loses  its  peritoneal  investment  and  becomes 
attached  by  connective  tissue  to  the  ventral  surface  of  the  left 
kidney. 

3.  The  ventral  surface  of  the  body  of  the  pancreas  is  in  the 
adult  lined  by  peritoneum  of  the  "lesser  sac"  ;  in  other  words 
the  organ  has  practically  assumed  a  ''  retro-peritoneal "  position, 
its  ventral  peritoneal  covering  appearing  now  as  the  dorsal  parietal 
peritoneum  of  the  retro-gastric  space. 

4.  When  completely  developed  the  extreme  end  (tail)  of  the 
pancreas  extends  to  the  left,  following  the  splenic  artery,  until  it 
touches  the  mesal  aspect  of  the  spleen  at  the  hilus. 

5.  If  we,  therefore,  leave  out  of  consideration  for  the  moment 
the  transverse  colon  and  duodenum,  which  will  be  taken  up 
presently,  and  confine  ourselves  to  the  arrangement  of  the 
stomach,  pancreas  and  great  omentum,  a  sagittal  section 
to  the  left  of  the  median  line  would  result  as  shown  in 
Fig.  222,  after  the  adult  condition  of  adhesion  has  been  estab- 
lished. 

The  same  process  of  fixation,  which  resulted  in  the  anchoring  of 
duodenum  and  head  of  pancreas,  extends^ to  the  body  of  the  gland 
and  the  investing  omentum.  The  peritoneum  lining  the  original 
left,  now  the  dorsal  surface  of  the  gland,  fuses  with  the  primitive 
parietal  peritoneum  covering  the  diaphragm  and  the  left  kidney. 
The  main  body  of  the  pancreas  in  the  adult  appears  prismatic, 
giving  a  triangular  sagittal  section.  The  dorsal  surface  is  adherent 
to  the  ventral  surface  of  the  left  kidney ;  the  ventral  surface  is 
covered  by  the  secondary  parietal  peritoneum  (original  right  layer 
of  mesogastrium)  which  lines  the  dorsal  wall  of  the  retrogastric 
space  and  omental  bursa  (lesser  peritoneal,  sac).     The  great  omen- 


126  ANATOMY  OF   THE  PERITONEUM. 

turn  now  appears  to  take  its  dorsal  point  of  departure  along  the 
sharp  margin  which  separates  this  ventral  surface  of  the  pancreas 
from  a  third  narrower  surface  directed  caudad.  This  surface, 
under  the  conditions  which  we  are  at  present  examining, 
would  be  hned  by  the  peritoneum  continued  onto  it  from  the 
dorsal  layer  of  the  great  omentum.  This  peritoneum  merges 
along  the  dorsal  margin  of  this  caudal  surface  of  the  pancreas 
with  the  general  parietal  peritoneum  covering  the  left  lumbar 
region  and  the  caudal  part  of  ventral  surface  of  the  left  kid- 
ney. We  have,  therefore,  along  this  line  a  secondary  tran- 
sition from  visceral  to  parietal  peritoneum,  obtained  by  the 
obliteration  of  the  original  visceral  peritoneum  investing  the 
dorsal  surface  of  the  pancreas  before  adhesion  to  the  parietal 
peritoneum. 

The  pancreas  assumes,  therefore,  in  the  adult  a  secondary  retro- 
peritoneal position,  covered  on  its  ventral  surface  by  peritoneum 
of  the  "lesser  sac,"  while  the  caudal  surface  is  lined  by  part  of 
the  general  peritoneal  membrane  of  the  "greater  sac."  The  dor- 
sal surface,  denuded  of  serous  covering  by  obliteration,  is  adherent 
to  the  crura  of  the  diaphragm,  the  aorta  and  the  ventral  surface 
of  the  left  kidney. 

It  is  now  proper  to  compare  the  conclusions  just  derived  from 
the  study  of  the  development  of  the  human  dorsal  mesogastrium 
and  connected  structures  (spleen  and  pancreas)  with  the  condi- 
tions presented  by  the  corresponding  parts  in  one  of  the  lower 
mammalia,  which  illustrate  some  of  the  human  embryonal 
stages.  Here  again  the  abdominal  cavity  of  the  cat  forms  an 
instructive  object  of  study. 

The  purpose  of  the  following  comparison  should  be  twofold : 

I.  The  mesogastrium,  spleen  and  pancreas  in  the  cat  will 
clearly  illustrate  the  process  of  human  development  above  out- 
lined. 

II.  The  abdominal  viscera  of  the  cat,  if  properly  arranged, 
will  enable  us  to  complete  the  consideration  of  this  region  by  in- 
cluding the  very  important  relations  which  the  transverse  colon 


SPLEEN,  PANCREAS  AND   GREAT  OMENTUM  OF  CAT.  127 

and  third  portion  of  the  duodenum  bear  in  man  to  the  great 
omentum  and  pancreas. 

I.    SPLEEN,  PANCREAS   AND   GREAT   OMENTUM   OF  CAT. 

After  opening  the  abdominal  cavity  it  will  be  seen  that  the 
great  omentum  can  be  lifted  up,  exposing  the  subjacent  coils  of 
the  small  and  large  intestine,  to  which  it  adheres  at  no  point. 
In  other  words  the  entire  dorsal  surface  of  that  part  of  the  original 
mesogastrium  which  forms  the  great  omentum  is  free.  It  will  be 
remembered  that  this  is  not  the  case  in  the  adult  human  subject, 
because  here  the  dorsal  surface  of  the  great  omentum  adheres  to 
the  transverse  colon.  Consequently  in  man  only  that  portion  of 
the  dorsal  surface  of  the  omentum  can  be  seen  which  extends 
between  the  transverse  colon  and  the  caudal  free  edge  of  the 
membrane. 

It  will  be  noted  that  on  the  left  side  the  spleen  is  connected  by 
its  mesal  surface  to  the  omentum  and  through  it  with  the  stomach 
(gastro-splenic  omentum).  In  other  words  the  cat  illustrates  the 
human  embryonal  stage  in  which  the  spleen  has  appeared  between 
the  layers  of  the  dorsal  mesogastrium  at  the  extreme  left  or  blind 
end  of  the  retrogastric  pouch  formed  by  the  rotation  of  the  stomach 
and  elongation  of  the  mesogastric  membrane,  but  before  the  ad- 
hesion has  taken  place  between  the  original  left  (now  dorsal)  layer 
of  the  vertebro-splenic  segment  of  the  mesogastrium  and  the 
primitive  parietal  peritoneum  apposed  to  it  (Fig.  219).  Con- 
sequently the  dorsal  wall  of  the  "lesser"  sac  in  the  cat  is  still 
composed  of  the  two  layers  of  the  free  vertebro-splenic  segment 
of  the  mesogastrium,  the  primitive  right  (now  ventral)  layer  not 
having  been  converted,  as  is  the  case  in  man,  into  secondary 
parietal  peritoneum  by  adhesion  of  the  original  left  (now  dorsal) 
layer  to  the  primitive  prerenal  parietal  peritoneum. 

If  we  now  examine  the  relation  of  the  pancreas  to  the  perito- 
neum we  can  estabHsh  the  following  facts : 

1.  The  portion  of  the  gland  adjacent  to  the  duodenum,  corre- 
sponding to  the  "  head  "  of  the  human  organ,  is  included  between 


128  ANATOMY  OF  THE  PERITONEUM. 

the  two  layers  of  the  mesoduodenum.  This  membrane  is  free, 
so  that  the  dorsal  surface  of  this  portion  of  the  pancreas  is  seen 
to  be  invested  by  the  dorsal  layer  of  the  mesoduodenum  (Fig. 
223).  The  duodenum  and  the  mesoduodenum,  the  latter  con- 
taining the  head  of  the  pancreas  between  its  layers,  can  be  turned 
toward  the  median  line,  so  as  to  expose  the  entire  ventral  surface 
of  the  post-cava  and  right  kidney.  To  illustrate  the  arrange- 
ment which  is  found  in  the  adult  human  subject  the  descending 
duodenum  and  pancreas  should  be  allowed  to  fall  over  to  the 
right  so  as  to  cover  the  vena  cava  and  the  mesal  part  of  the  ventral 
surface  of  right  kidney.  The  adult  human  condition  will  now  be 
produced  if  we  assume  that  the  structures  are  fixed  in  this  posi- 
tion by  the  obliteration  of  the  apposed  serous  surfaces,  viz.,  the 
parietal  peritoneum  over  kidney  and  vena  cava  on  the  one  hand 
and  the  right  layer  of  the  mesoduodenum  and  the  dorsal  visceral 
peritoneum  of  the  duodenum  on  the  other. 

2.  In  following  out  the  pancreas  of  the  cat  in  its  entire  extent, 
proceeding  to  the  left  of  the  pylorus,  it  will  be  seen  that  the 
body  of  the  gland  has  extended  between  the  two  dorsal  layers 
of  the  great  omentum  (primitive  dorsal  mesogastrium)  over  to 
the  spleen  (Fig.  223).  Consequently  the  arrangement  in  the 
cat  corresponds  to  the  stage  in  the  human  development  shown 
in  Fig.  219  and  Fig.  221  in  which  adhesion  of  the  dorsal  surface 
of  the  pancreas  to  the  parietal  peritoneum  has  not  yet  taken  place. 

It  will  be  quite  easy  to  reconstruct  from  the  facts  as  demon- 
strated by  the  arrangement  of  the  parts  in  the  cat,  the  stage  in 
the  development  of  the  lesser  peritoneal  sac  in  which  the  dorsal 
wall  of  the  space  is  still  formed  by  the  proximal  portion  of  the 
free  dorsal  mesogastrium  (great  omentum)  and  the  structures  in- 
cluded between  its  two  layers. 

It  must  then  become  apparent  that  the  entire  serous  surface 
which  in  the  adult  human  subject  we  regard  as  "  parietal  perito- 
neum of  the  lesser  sac"  lining  the  dorsal  wall  of  the  retrogastric 
space  is  derived  from  what  originally  was  the  right  layer  of  the 
primitive  sagittal  dorsal  mesogastrium. 


OBEAT  OMENTUM,    TRANSVERSE  COLON  AND  DUODENUM.       129 

II.  RELATION  OF  GREAT  OMENTUM  TO  TRANSVERSE  COLON, 
TRANSVERSE  MESOCOLON  AND  THIRD  PART  OF  DUODENUM. 

The  second  purpose  to  be  accomplished  by  the  study  of  the 
cat's  abdominal  cavity  at  this  stage  is  the  correct  appreciation  of 
the  adult  human  conditions  which  are  produced  by  areas  of  ad- 
hesion between  the  transverse  colon,  transverse  mesocolon  and 
third  part  of  the  duodenum  on  the  one  hand,  and  the  dorsal 
mesogastrium,  as  great  omentum,  with  the  structures  contained 
betAveen  its  layers,  on  the  other. 

Perform  the  manipulations  of  the  large  and  small  intestine  in 
the  cat  (see  p.  67)  which  are  required  in  order  that  the  tract  may 
be  arranged  so  that  it  will  correspond  in  general  to  the  topo- 
graphical conditions  presented  by  the  adult  human  subject. 
Locate  the  transverse  colon  and  mesocolon  and  the  third  portion 
of  the  duodenum  produced  by  these  manipulations  in  imitation 
of  the  corresponding  human  structures.  Then  proceed  to  plot 
the  different  parts  out  successively  as  they  would  appear  in  a 
sagittal  section  (Fig.  224). 

The  following  facts  are  to  be  noted  and  indicated  on  the  plan 
of  the  section  : 

1.  The  great  omentum  is  free,  hanging  down  from  the  greater 
curvature  of  the  stomach  over  the  coils  of  intestine.  Turning  the 
omentum  up  it  will  be  observed  that  the  body  of  the  pancreas  is 
included  between  the  two  dorsal  layers  of  the  membrane. 

2.  The  omentum,  containing  the  pancreas,  can  be  lifted  up, 
exposing  the  next  succeeding  structure,  viz.,  the  transverse  colon 
and  mesocolon.  In  the  cat  the  large  intestine  has  been  brought 
over,  by  the  manipulations  above  indicated,  into  a  transverse  posi- 
tion so  as  to  represent  the  human  transverse  colon  and  its  meso- 
colon. It  is  therefore  necessary  to  remember  that  in  this  mammal 
the  fixation  of  the  transverse  mesocolon  in  the  position  indicated, 
by  adhesion  of  ascending  and  descending  mesocola  to  the  parietal 
peritoneum  of  the  abdominal  background,  has  not  yet  occurred. 
Consequently  the  membrane  must  be  held  in  the  transverse  posi- 
tion in  order  to  represent  the  human  arrangement. 

9 


130  ANATOMY  OF  THE  PERITONEUM. 

It^vill  of  course  be  observed  that  both  surfaces  of  the  transverse 
mesocolon  estabhshed  in  this  way  are  free,  not  adherent  to  either 
omentum  or  pancreas  on  the  one  hand,  nor  to  the  transverse  duo- 
d^enum  on  the  other. 

3.  The  third  or  transverse  portion  of  the  duodenum  is  seen  to 
be  attached  by  the  distal  part  of  the  mesoduodenum,  both  of  the 
serous  surfaces  of  the  membrane  being  free.  The  duodenum  hav- 
ing been  brought  from  right  to  left  transversely  across  vertebral 
column  and  aorta,  underneath  the  superior  mesenteric  artery,  the 
mesoduodenum,  in  the  segment  corresponding  to  the  transverse 
duodenum,  exchanges  its  original  sagittal  position  for  one  in  a 
horizontal  plane,  with  cephalic  (primitive  left)  and  caudal  (primi- 
tive right)  surfaces. 

Now  compare  the  above  arrangement  of  the  intestines  and 
peritoneum  in  the  cat  at  once  with  the  conditions  presented  in  the 
adult  human  subject,  reserving  certain  intermediate  stages,  as  ex- 
hibited by  some  of  the  lower  monkeys,  for  subsequent  study. 

The  examination  of  a  similar  sagittal  section  representing  sche- 
matically the  adult  human  arrangement  of  the  parts  (Fig.  225)  will 
reveal  the  following  points  of  difference  as  compared  with  the  cat : 

1.  The  peritoneum  covering  the  dorsal  surface  of  the  pancreas, 
derived  from  the  primitive  dorsal  mesogastrium,  has  become 
adherent  to  the  parietal  peritoneum,  as  previously  described. 

2.  The  cephalic  surfaces  of  the  transverse  colon  and  meso- 
colon fuse  with  the  corresponding  area  of  the  dorsal  (4th)  layer 
of  the  great  omentum  (dorsal  mesogastrium). 

In  the  human  foetus  in  the  4  th  month  the  connection  is  still 
so  slight  that  the  omentum  can  readily  be  separated  from  the 
transverse  colon  and  mesocolon. 

Further  dorsad  the  cephalic  layer  of  the  transverse  mesocolon 
adheres  to  the  serous  investment  of  the  caudal  surface  of  the 
pancreas,  derived,  as  we  have  seen,  from  the  same  dorsal  layer 
of  the  great  omentum. 

3.  The  duodenum  and  mesoduodenum  are  fixed  by  adhesion 
on  the  one  hand  to  the  parietal  peritoneum,  on  the  other  to  the 


OREAT  OMENTUM,  TRANSVERSE  COLON  AND  DUODENUM.       131 

caudal  layer  of  the  transverse  mesocolon  near  the  root  of  that 
membrane. 

4.  The  cavity  of  the  omental  bursa  is  usually  obliterated  in  the 
adult  caudad  of  the  level  of  the  transverse  colon,  by  adhesion  of 
the  apposed  surfaces  of  the  two  intermediate  omental  layers. 

We  have  therefore  three  general  areas  of  secondary  peritoneal 
adhesion  to  deal  with  (Fig.  225),  viz : 

1.  Dorsal  layer  of  primi- 
tive mesogastrium  (great 
omentum)  including  the 
serous  investment  of  the 
dorsal  and  caudal  surfaces 
of  the  pancreas  (Fig.  225,  1). 

2.  Transverse  duodenum 
and  mesoduodenum  (Fig. 
225,  2). 


to 


Parietal  peritoneum,  ce- 
phalic layer  of  transverse 
mesocolon  and  cephalic  sur- 
face of  transverse  colon. 


to 


Parietal  peritoneum  and 
caudal  layer  of  transverse 
mesocolon. 

3.  Between  the  apposed  serous  surfaces  of  the  intermediate 
omental  layers  (Fig.  225,  3). 

These  areas  of  adhesion  result  naturally  in  the  production  of 
secondary  lines  of  peritoneal  transition  as  follows  : 

1.  Figs.  225,  1 ;  226, 1,  from  the  omentum,  dorsal  layer,  to  the 
caudal  surface  of  transverse  colon,  caudal  layer  of  transverse  meso- 
colon and  caudal  surface  of  the  pancreas. 

2.  Figs.  205,  2;  226,  2,  from  the  caudal  layer  of  the  trans- 
verse mesocolon  across  the  transverse  portion  of  the  duodenum 
to  the  parietal  peritoneum  and  mesentery  of  the  jejuno-ileum. 

3.  Figs.  225,  3;  226,  3,  between  the  intermediate  omental  lay- 
ers, forming  the  secondary  caudal  Hmit  of  the  lesser  sac. 

These  changes  consequently  result  in  the  rearrangement  of  the 
adult  human  peritoneum  in  accordance  with  the  following 
schema  (Fig.  226) : 

We  trace  the  peritoneum  as  the  ventral  or  superficial  layer  of 
the  great  omentum  from  the  greater  curvature  of  the  stomach 
caudad  around  the  distal  free  edge  of  the  omentum  and  cephalad, 
as  the  dorsal  layer,  to  the  ventral  border  of  the  transverse  colon. 


132  ANATOMY  OF  TEE  PERITONEUM. 

Here  apparently  this  layer  is  continued  across  the  caudal  surface  of 
the  large  intestine  and  beyond  as  the  caudal  layer  of  the  transverse 
mesocolon.  While  this  condition  obtains  practically  in  the  adult 
it  is  to  be  remembered  that  the  adhesion  (at  1  in  Fig.  225)  pre- 
vents us  from  lifting  the  omentum  away  from  the  colon,  and  that 
consequently  the  apparent  continuity  of  the  dorsal  layer  of  the 
great  omentum  with  the  caudal  layer  of  the  transverse  mesocolon 
is  the  result  of  this  peritoneal  fusion. 

Near  the  dorsal  attachment  or  "  root "  of  the  transverse  meso- 
colon the  caudal  layer  of  the  membrane  becomes  continuous 
with  the  parietal  peritoneum  investing  the  transverse  portion  of 
the  duodenum  on  its  ventral  aspect,  which  peritoneum  in  turn 
passes  into  the  free  mesentery  of  the  jejuno-ileum  (Fig.  225,  2). 
Comparison  with  the  previous  figures  will  show  that  we  are  deal- 
ing here  with  another  area  of  secondary  peritoneal  fusion. 

If  we  now  open  the  "  lesser  peritoneal  cavity  "  by  dividing  the 
two  layers  of  the  omentum  attached  to  the  greater  curvature  of 
the  stomach  (Figs.  225  and  226  in  direction  of  arrow)  we  will 
apparently  reach  the  upper  or  cephalic  surface  of  the  transverse 
mesocolon.  This  layer  can  be  followed  dorsad  to  the  sharp 
border  which  separates  the  ventral  and  caudal  surfaces  of  the 
pancreatic  body  and  the  membrane  can  be  traced  thence  over  the 
ventral  surface  of  the  gland  to  the  diaphragm.  (The  connections 
with  the  liver  and  stomach  shown  schematically  in  the  diagram 
(Fig.  225)  are  to  be  considered  in  detail  subsequently.) 

In  the  adult  the  peritoneal  surface  just  described  appears  as  the 
cephalic  layer  of  the  transverse  mesocolon  and  its  continuation 
dorsad.  From  the  facts  previously  considered  it  will  be  at  once 
apparent  that  we  are  really  dealing  here  with  a  part  of  the  third 
layer  of  the  primitive  omentum.  We  do  not  see  the  original 
cephalic  layer  of  the  transverse  mesocolon.  This  membrane  has 
become  fused  with  the  fourth  omental  layer,  and  its  free  serous 
surface  obliterated  in  the  stretch  between  the  vertebral  column 
and  the  transverse  colon.  Hence  the  human  adult  transverse 
mesocolon  is  apparently  composed  of  two  layers ;  the  cephalic  of 


RELATIONS  OF  GREAT  OMENTUM.  133 

these  layers  appears  as  peritoneum  of  the  "lesser  sac,"  in  conform- 
ity with  its  derivation  from  the  original  third  omental  layer  lining 
the  interior  of  the  omental  bursa.  The  caudal  layer,  on  the  other 
hand,  is  a  part  of  the  general  or  ''greater"  peritoneal  membrane. 
The  entire  adult  transverse  mesocolon,  hence,  comprises /our  peri- 
toneal layers,  of  which  only  two  remain  as  permanently  free 
serous  surfaces.  These  differ  in  their  derivation,  the  cephalic 
layer  being  a  part  of  the  primitive  dorsal  mesogastrium  (third 
omental  layer),  while  the  caudal  layer  is  part  of  the  primitive 
mesocolon.  Between  these  two  layers  of  the  adult  transverse 
mesocolon  are  included  the  two  obliterated  embryonic  mem- 
branes, viz.,  the  fourth  omental  layer  and  the  original  dorsal  layer 
of  the  transverse  mesocolon. 

Caudad  the  two  layers  of  the  adult  transverse  mesocolon  sur- 
round the  transverse  colon  and  are  continuous  along  the  ventral 
margin  of  the  intestine  with  the  layers  of  the  great  omentum. 
Toward  the  vertebral  column  these  layers  again  diverge.  The 
cephalic  layer,  lining  the  "lesser  peritoneal  cavity "  invests  the 
ventral  surface  of  the  pancreas.  The  caudal  layer  continues  over 
the  caudal  surface  of  the  body  of  the  gland  and  transverse  portion 
of  the  duodenum  into  the  parietal  peritoneum  and  the  free  mes- 
entery of  the  jejuno-ileum.  Consequently  the  returning  layers 
of  the  great  omentum  are  said  to  surround  the  transverse  colon 
and  unite  along  the  dorsal  border  of  the  intestine  to  form  the 
transverse  mesocolon,  which  membrane  is  continued  dorsad  to- 
ward the  vertebral  column  as  two  layers.  At  the  "root"  of  the 
transverse  mesocolon  these  layers  are  then  described  as  diverging, 
the  cephalic  passing  up  to  line  the  ventral  surface  of  the  pancreas, 
while  the  caudal  continues  over  the  caudal  surface  of  the  pancreas 
and  third  portion  of  the  duodenum  into  the  parietal  peritoneum 
and  mesentery. 

Wherever  in  this  discussion  of  the  transverse  mesocolon  the 
transition  between  the  caudal  layer  of  the  membrane  and  the 
"parietal"  peritoneum  is  referred  to  it  is  necessary  to  remember 
that  this  "parietal"  peritoneum  is  the  secondary  investment  of 


134  ANATOMY  OF  THE  PERITONEUM. 

the  abdominal  background,  formed  by  the  surface  of  the  ascend- 
ing and  descending  mesocolon  which  remains  free  after  the  oppo- 
site surface  and  the  vertical  segments  of  the  large  intestine  have 
been  anchored  by  adhesion  to  the  primary  parietal  peritoneum 
(cf.  p.  81,  Fig.  158). 

A  summary  at  this  point  of  the  course  of  the  dorsal  mesogas- 
trium,  in  forming  the  great  omentum  and  its  subsequent  connec- 
tions, would  show  us  that  the  membrane  first  enlarges  and  de- 
scends towards  the  transverse  colon  (Fig.  177).  The  omental 
bag  is  formed  by  the  descending  or  superficial  segment  (starting 
from  the  greater  curvature  of  the  stomach),  turned  toward  the 
observer  in  the  figure,  and  by  the  ascending  or  deep  layer  which 
is  attached  above  to  the  dorsal  abdominal  wall,  in  front  of  the 
vertebral  column  and  aorta  along  the  original  line  of  origin  of 
the  dorsal  mesogastrium.  Gradually  growing  and  descending 
further,  the  deep  segment  becomes  attached  to  the  transverse 
colon.  It  also  becomes  connected,  especially  on  the  left  side,  with 
the  diaphragmatic  peritoneum  (phrenicocolic  lig.),  so  that  its 
original  starting  point  is  no  longer  distinct.  Finally  the  devel- 
opment of  the  spleen  and  pancreas  between  the  layers  of  the  dor- 
sal segment  and  their  subsequent  connections  obscure  the  origi- 
nal conditions. 

Fig.  297  shows  the  primitive  condition  at  a  time  when  the  con- 
nection with  the  transverse  colon  and  mesocolon  has  not  yet 
taken  place. 

The  omental  bag  or  bursa  epiploica  develops  in  the  region  of 
the  dorsal  mesogastrium  and  the  viscera  included  between  its 
layers,  by  changes  in  the  position  and  extent  of  the  membrane 
which  finally  result  in  placing  a  part  of  the  right  half  of  the 
primitive  ccelom  cavity  behind  the  stomach.  Up  to  the  sixth  week 
the  line  of  origin  of  the  dorsal  mesogastrium  is  from  the  mid- 
dorsal  line  of  the  abdomen.  It  deviates  from  this  origin  to  the 
left  because  the  great  curvature  of  the  stomach  to  which  it  is 
attached  turns  in  this  direction.  On  this  account,  and  because  of 
the  rapid  growth  of  this  portion  of  the  mesogastrium,  a  bag  or 


SUMMARY  OF  CHANGES  IN  DORSAL  MESOGASTRIUM.  135 

space  is  formed  behind  the  stomach.  The  entrance  into  this  space 
is  situated  to  the  right  of  the  lesser  curvature,  behind  the  peri- 
toneal layers  connecting  the  same  with  the  liver  (lesser  or  gastro- 
hepatic  omentum  and  hepato-duodenal  ligament).  The  ventral 
wall  of  this  space  is  formed  by  the  dorsal  surface  of  the  stomach 
itself,  the  dorsal  wall  by  the  mesogastrium,  turning  to  the  left 
and  presenting  its  original  right  surface,  now  directed  ventrad. 
The  caudal  limit  of  the  retro-gastric  space  is  given  by  the  turn  of 
the  mesogastrium  to  reach  its  attachment  along  the  greater  cur- 
vature of  the  stomach  (rudiment  of  great  omentum). 

The  stomach,  in  contributing  to  produce  these  changes,  passes 
from  the  vertical  to  the  oblique  and  finally  into  the  transverse 
position.  The  pylorus,  formerly  directed  caudad,  passes  up  and 
to  the  right.  The  fundus  develops  and  the  original  left  side  of 
the  stomach  becomes  the  ventral,  the  right  side  the  dorsal.  The 
original  dorsal  border,  now  the  greater  curvature,  moving  caudad, 
carries  the  attached  dorsal  mesogastrium  with  it  into  its  new 
position.  The  mesogastrium  now  pouches  to  form  the  great 
omentum  and  rapidly  enlarges.  At  first  hardly  projecting  be- 
yond the  greater  curvature,  it  increases  in  length  until  it  forms 
a  four-layered  apron  which  hangs  down  as  a  loose  sac  over  the 
transverse  colon  and  the  coils  of  the  small  intestine  (Fig.  177). 
In  the  foetus  of  six  months  the  cavity  of  the  omental  bag  ex- 
tends caudad  as  far  as  the  lower  edge  of  the  omentum.  Later 
adhesions  between  the  peritoneal  surfaces  lining  the  interior  of 
the  bursa  limit  this. extension. 

The  omental  bursa  is  therefore  formed  by  a  ventral  lamella, 
consisting  of  two  peritoneal  layers,  which  hangs  down  from  the 
greater  curvature  of  the  stomach  and  passes  around  the  caudal 
free  edge  of  the  omentum  into  the  double-layered  dorsal  lamella, 
which  ascends,  over  the  transverse  colon,  to  the  original  starting 
point  of  the  dorsal  mesogastrium  along  the  front  of  the  vertebral 
column  and  aorta.  Hence  the  "  great  omentum  "  is  originally 
composed  of  four  layers  of  peritoneum. 

The  dorsal  double  lamella  becomes  adherent  over  a  consider- 


136  ANATOMY  OF  THE  PERITONEUM. 

able  area  to  the  parietal  peritoneum  of  the  dorsal  abdominal  wall. 
In  this  way  the  organs  developed  between  the  two  layers  of  the 
lamella  obtain  their  final  fixed  position.  The  pancreas  becomes 
anchored  and  appears  in  the  adult  as  a  ''  retro-peritoneal "  struc- 
ture, while  the  spleen  is  attached  by  the  "  phrenico-lienal  liga- 
ment "  to  the  diaphragm. 

In  addition  the  dorsal  omental  lamella  adheres  in  the  fourth 
month  to  the  cephalic  layer  of  the  transverse  mesocolon  and  to 
the  transverse  colon. 

Important  illustrations  of  some  of  the  intermediate  stages  in  the 
human  development  of  this  portion  of  the  peritoneal  tract  are 
afforded  by  the  permanent  adult  conditions  found  in  the  abdom- 
inal cavity  of  some  of  the  lower  primates,  notably  certain  of  the 
cynomorphous  monkeys. 

Fig.  227  shows  the  abdominal  cavity  and  disposition  of  the 
peritoneum  in  a  macaque  monkey  {Macacus  rhesus,  ^ )  in  the  ven- 
tral view,  with  the  coils  of  small  intestines  removed  and  the  omen- 
tum lifted  up  and  reflected  upon  the  ventral  body  wall.  The  fol- 
lowing important  points  of  difference  from  the  arrangement  in  the 
cat  on  the  one  hand,  and  in  man  on  the  other,  are  to  be  noted : 

1.  The  large  intestine  presents  the  typical  primate  course,  with 
an  ascending,  transverse  and  descending  colon.  The  ileo-csecal 
junction  is  situated  in  the  right  iliac  fossa. 

2.  The  ascending  and  descending  mesocola  are  still  free,  not 
having  become  adherent  to  the  parietal  peritoneum  along  the 
dorsal  abdominal  wall.  Hence  the  caudal  portions  of  the  ventral 
surfaces  of  the  two  kidneys  are  still  covered  by  the  primitive 
parietal  peritoneum. 

3.  The  great  omentum  is  not  yet  adherent  to  the  transverse 
colon  and  mesocolon  except  for  a  short  distance  on  the  extreme 
right.  At  this  point  the  dorsal  layer  of  the  omentum  has  begun 
to  contract  adhesions  to  the  hepatic  flexure  of  the  colon  and  as- 
cending colon,  but  the  rest  of  the  transverse  colon  is  free.  Dif- 
fering from  the  human  arrangement  is  a  line  of  adhesion, 
uniformly  present  in  these  monkeys,  between  the  dorsal  surface 


PLATE    CXIII. 


PANCREAS 


TRANSV. 
COLON 


Fig.  230. — Arrangement  of  great  omentum  as  found  in  Mamma 
rhcsHf!,  shown  without  reference  to  areas  of  peritoneal  obliteration. 


STOMACH 


PANCREAS 


Fig.  2.'!1.— Corresponding  section  of  human  adult  peritoneum 
showing,  along  dotted  lines,  area  of  peritoneal  adhesion. 


\ 


PLATE    CXIV. 


DIAPHRAGM 


STOMACH 


PANCREAS 


Fig.  232. — Section  showiug  human  adult  peritoneum  without 
reference  to  area  of  adhesion. 


PANCREAS 


Figs.  233-235. — Series  of  schematic  sagittal  sections  through  left 
kidney  and  adrenal,  pancreas,  and  transverse  colon,  to  show  develop- 
ment of  adult  peritoneal  relations. 

Fig.  233. — Embryonic  condition,  as  illustrated  by  cat,  after  rotation 
of  intestine.  Pancreas  free  between  dorsal  layers  of  great  omentum. 
Tansverse  colon  and  mesocolon  free.  Kidney  behind  primitive  parietal 
peritoneum. 


PLATE    CXV. 


PANCREAS 


Fig.  234. — Area  of  adhesion  between :   1.  Primitive  parietal  perito- 
neum.   2.  Mesogastrium  forming  great  omentum.    3.  Colon  and  mesocolon. 


Fig.  235. — Adult  human  arrangement,  shown  without  reference 
to  obliterated  areas. 


PLATE    CXVI. 


GREAT 

OMENTUM 

RAISED 


HEPATIC 

FLEXURE 

OF   COLON 

TRANSVERSE 
COLON 


PANCREAS 


L.    KIDNEY 

FREE    DE- 
SCENDING 
MESOCOLON 


Fig.  236.— Abdominal  viscera  of  Macacus  cyuomolgus,  Kr:i  monkey. 
Museum,  No.  1801.) 


(Columbia  Uuiversity 


PLATE    CXVII. 


ECTODERM 


NOTOCHOR^ 


HEPATIC  POUCH 


ORAL    PLATE 


Fig.  237. — Longitudinal  section   of  an  embryo  of  Petromyzon 
planeri,  four  days  old.     (Minot,  after  KupflPer.) 


RIGHT    LOBE 
OF    LIVER 


ILEO-COLIC 
JUNCTION 


SMALL 
INTESTINE 


CESOPHAGU8 


STOMACH 


LEFT    LOBE 
OF    LIVER 


Fig.  238. — Fseudemys  elegans,  pond  turtle.    Alimentary  canal.    (Columbia  University  Museum, 
No.  1437.) 


PLATE    CXVllI. 


GALL-BLADDER 


STOMACH 


-_   MID-GUT 


Fig.  239. — Stomach,  mid-gut,  pancreas,  and  liver 
of  Boa  constrictor,  boa.  (Columbia  University  Mu- 
seum, No,  1832.) 


PLATE    CXIX. 


Fig.  240. — Liver  of  Macacus  cynomolgm,  Kra  monkey. 
(Columbia    University  Museum,  No.  xf  1^-) 


Fig.  241.— Liver  of  Pleuronectes  maculatus,  flounder. 
(Columbia  University  Museum,  No.  1679.) 


PLATE    CXX. 


COMMON 
BILE-DUCT 


DUODENUM 


Fig.  242. — Schema  of  hepatic  and  cys- 
tic ducts.      (Nuhn.) 


COMMON 
DUCT 


DUODENUM 


Fig.   243. — Schema   of   hepatic    and    cystic 
ducts.     (Nuhn.) 


GALL- 
BLADDER 


COMMON 
DUCT 


HEPATICO- 

CYSTIC 

DUCT 


DUODENUM 


Fig.  244. — Schema  of  hepatic  and  cys- 
tic ducts.     (Nuhn.) 


CYSTICO- 

ENTERIC 

DUCT 


HEPATICO- 
CYSTIC  DUCT 


HEPATICO- 
ENTERIC  DUCT 


DUODENUM 


Fig.   24.5. — Schema    of   liepatic  and    cystic 
ducts.     (Nuhn.) 


PRECARDINAL 
VEIN 

DUCT    OF 

CUVIER 

SUBCLAVIAN 

VEIN 

VITELLINE 
VEINS 


VITELLINE 
ARTERIES 


allantoic 

(hypogastric) 

arteries 


CAROTID 
ARTERIES 


BRANCHIAL 
ARCHES 


AORTIC  ROOT 
HEART 


SUBCLAVIAN 
ARTERY 


POSTCARDI 
NAL  VEIN 


COMMON 
ILIAC  ART 
EXT.    ILIAC 
ART. 


CAUDAL    ART 


Fig.  246. — Diagram  of  erahryonic  vascular  system,  without  the  portal  circulation.  (Parker, 
after  Wiedersheim.)  The  dorsal  aorta  is  formed  by  the  junction  of  the  right  and  left  aortic  roots 
arising  from  the  confluence  of  the  branchial  arterial  arches. 


PERITONEUM  IN  MACAGUS  RHESUS.  137 

of  the  omentum  along  its  right  edge  and  the  ventral  surface 
and  right  border  of  the  csecum  and  ascending  colon,  parts  which 
normally  are  not  adherent  to  the  omentum  in  man. 

4.  Hence  in  tracing  the  omentum  to  the  left  of  the  limited 
adhesion  to  the  hepatic  flexure  and  ascending  colon,  i.  e.,  nearly 
throughout  the  entire  extent  of  the  transverse  colon,  we  find 
the  membrane  passing  freely  without  adhesion  over  the  cephalic 
surface  of  the  transverse  mesocolon,  which  preserves  its  original 
free  condition,  independent  of  the  omentum.  This  arrangement 
is  shown  in  the  schematic  sagittal  section  in  Fig.  230. 

5.  Tracing  the  omentum  dorsad  beyond  the  transverse  colon 
and  mesocolon  the  pancreas  is  reached.  Here  we  encounter  the 
first  extensive  area  of  omental  or  mesogastric  adhesion.  The 
omental  peritoneum  continues  over  the  ventral  and  caudal  sur- 
faces of  the  gland,  investing  the  same,  but  the  dorsal  surface  has 
lost  its  serous  covering  and  is  anchored  to  the  ventral  surface  of 
the  left  kidney.  Hence  a  sagittal  section  would  show  the  arrange- 
ment of  the  monkey's  omentum  as  indicated  in  the  schematic 
Figs.  229  and  230.  Making  now  a  general  comparison  of  the' 
peritoneal  membrane  of  this  animal  with  that  of  man,  and  of  both 
with  the  preceding  common  embryonal  condition,  we  can  draw 
the  following  conclusions,  indicated  schematically  in  the  five 
figures  228-232. 

1.  The  dorsal  layer  of  the  monkey's  omentum  in  its  proximal 
segment  behaves  in  the  same  way  as  in  man,  i.  e.,  it  becomes  ad- 
herent to  the  primitive  parietal  peritoneum  down  as  far  as  the 
caudal  margin  of  the  dorsal  surface  of  the  pancreas  included  be- 
tween the  primitive  mesogastric  layers  forming  by  their  further 
growth  the  omental  apron. 

Therefore  we  find,  as  in  the  human  subject, 

(a)  The  pancreas  adherent  to  the  ventral  surface  of  the  left 
kidney. 

(6)  A  portion  of  the  ventral  surface  of  the  kidney,  cephalad  of 
the  pancreas,  and  the  dorsal  wall  of  the  retrogastric  (lesser  peri- 
toneal) space  lined  by  secondary  parietal  peritoneum  derived  from 


138  AJSTATOMY  OF  THE  PERITONEUM. 

the  third  layer  of  the  omentum  (original  right  layer  of  dorsal 
mesogastrium). 

2.  The  monkey  differs  from  adult  man  in  the  behavior  of  the 
dorsal  omental  layer  in  relation  to  the  cephalic  surface  of  the 
transverse  mesocolon.  The  adhesion,  which  in  the  human  subject 
fuses  this  layer  with  the  transverse  colon  and  mesocolon,  does  not 
occur  in  the  monkey. 

Hence  we  have  in  this  animal  the  following  conditions : 

(a)  The  omentum  is  non-adherent  to  the  transverse  colon  and 
transverse  mesocolon. 

(6)  The  caudal  surface  of  the  pancreas  is  lined  by  its  original 
mesogastric  peritoneum. 

(c)  The  transverse  mesocolon  is  formed  by  the  original  two 
layers  of  the  primitive  dorsal  mesentery  ;  hence  its  cephalic  layer 
is  not  ''  peritoneum  of  the  lesser  sac  "  as  is  the  case  in  man. 

(d)  The  caudal  part  of  the  ventral  surface  of  the  left  kidney 
below  the  pancreas,  is  covered  by  the  original  parietal  peritoneum. 

(e)  Only  one  point  or  line  of  secondary  peritoneal  transition  exists, 
where  the  dorsal  layer  of  the  omentum  in  the  adult  becomes  con- 
tinuous with  the  parietal  peritoneum  covering  the  caudal  surface 
of  the  pancreas  and  the  ventral  surface  of  the  left  kidney. 

Note:  In  the  schematic  sections  shown  in  Figs.  228  to  232  the 
transverse  I  colon  is  represented  as  far  removed  from  the  ventral  sur- 
face of  the  left  kidney,  in  order  to  make  the  peritoneal  lines  of  the 
mesocolon  more  clear.  Actually  a  sagittal  section  which  would 
divide  the  kidney  would  cut  the  transverse  colon  at  its  extreme 
left  end,  where  it  turns  close  to  the  ventral  surface  of  the  left  kid- 
ney and  then  follows  its  lateral  border  to  form  the  splenic  flexure 
(Fig.  235).  The  caudal  part  of  the  ventral  surface  of  the  left 
kidney  in  the  adult  human  subject  is  covered  by  the  peritoneum 
which,  as  secondary  parietal  peritoneum,  is  derived  from  the 
upper  part  of  the  right  leaf  (later  ventral  leaf)  of  the  descending 
mesocolon.  Hence  it  should  be  remembered  that  these  diagrams 
present  combinations  of  sections.  A  section  which  will  show  the 
full  development  of  the  transverse  mesocolon  is  mesad  of  the 


SPLEEN  AND   OMENTUM  IN  MACAGUS  RHESUS.  139 

kidney ;  while  a  section  through  the  kidney  would  be  too  far  lat- 
erad  to  show  the  transverse  mesocolon. 

Figs.  233,  234  and  235  show  sagittal  sections  through  the  left 
kidney  with  the  adult  arrangement  of  the  peritoneum  and  colon 
and  the  embryonic  and  adhesion  stages  leading  to  the  same. 

It  will  be  observed  that  in  all  the  schematic  sections  of  the 
early  embryonic  stages  the  two  layers  of  the  transverse  mesocolon 
are  shown  without  dorsal  attachment,  as  turning  with  the  forma- 
tion of  a  fold  (Fig.  228  at  x)  into  two  layers  descending  ven- 
trad  of  the  parietal  peritoneum.  This  is  because  the  dorsal  at- 
tachment of  the  mesocolon  is  at  this  stage  still  in  the  median  Hne 
and  would  hence  not  be  encountered  by  a  sagittal  section  through 
the  kidney,  and  because  the  two  layers  of  the  transverse  meso- 
colon, immediately  after  rotation  of  the  large  intestine,  are  still 
directly  continuous  with  the  two  layers  of  the  descending  meso- 
colon. That  is  to  say,  the  cephalic  layer  of  the  transverse  meso- 
colon is  continuous  with  the  dorsal  (originally  the  left)  layer  of 
the  descending  mesocolon,  and  the  caudal  layer  of  the  transverse 
mesocolon  with  the  ventral  (originally  the  right)  layer  of  the 
descending  mesocolon,  which  is,  in  the  human  subject,  to  assume 
subsequently  the  character  of  parietal  peritoneum  after  the  dorsal 
layer  and  the  primitive  parietal  peritoneum  have  become  oblit- 
erated by  adhesion  (Fig.  235). 

Fig.  236  shows  this  continuity  of  the  descending  and  transverse 
mesocolon  as  a  permanent  adult  condition  in  the  macaque.  The 
fold  of  transition  between  the  two  is  seen  at  x  in  Fig.  228.  It 
will  be  noticed  that  the  ventral  surface  of  the  left  kidney,  caudad 
of  the  adherent  pancreas,  is  covered  by  the  primitive  parietal 
peritoneum,  corresponding  to  section  in  Fig.  230. 

RELATIONS  OF  SPLEEN  AND  OMENTUM  IN  MACACUS  BHESUS. 

The  spleen  in  this  animal  has  not  contracted  any  extensive 
adhesions  to  the  parietal  peritoneum  (the  phrenico-lienal  lig. 
of  anthropotomy  is  not  developed).  It  can  be  turned  mesad  so 
as  to  expose  the  lateral  border  and  an  adjacent  segment  of  the 


140  ANATOMY  OF  THE  PERITONEUM. 

ventral  surface  of  the  left  kidney,  as  well  as  the  dorsal  surface  of 
the  tail  of  the  pancreas  at  its  tip,  still  covered  by  mesogastric 
peritoneum.  Hence  in  the  monkey  the  adhesion  of  the  original 
vertebro-splenic  segment  of  the  mesogastrium,  including  the  pan- 
creas, to  the  primitive  parietal  peritoneum  is  less  complete  than 
in  man. 

MEDIAN  ATTACHMENT  OF  DESCENDING  MESOCOLON  AND  ITS 

RELATION  TO  THE  MESOCOLON  OF  THE  SIGMOID 

FLEXURE  IN  THE  MACAQUE. 

Fig.  236  shows  the  abdominal  viscera,  hardened  in  situ,  of 
Macacus  cynomolgus,  the  Kra  monkey,  in  the  ventral  view  and 
from  the  left  side. 

The  great  omentum  is  lifted  up,  the  pancreas  is  adherent  to  the 
ventral  surface  of  the  left  kidney,  the  caudal  portion  of  which  is 
covered  by  the  primary  parietal  peritoneum,  which  can  be  ex- 
posed by  turning  the  still  free  descending  mesocolon  mesad.  The 
mesocolon  retains  its  primitive  attachment  to  the  median  line 
ventrad  of  the  large  prevertebral  blood  vessels.  It  is  readily  seen 
that  adhesion  between  the  left  leaf  of  this  free  descending  meso- 
colon and  the  parietal  peritoneum  down  to  the  level  of  the 
iliac  crest  would  produce  the  conditions  found  in  the  human 
adult,  with  an  attached  descending  colon  and  a  free  sigmoid  flex- 
ure ;  also  that  limited  adhesion  of  the  mesocolon  of  the  sigmoid 
flexure  to  the  parietal  peritoneum  would  produce,  as  previously 
explained  (cf  p.  97),  the  intersigmoid  peritoneal  fossa. 

2.  Ventral  Mesogastrium  and  Liver. — The  peritoneal  reflections 
from  the  stomach  to  the  liver,  and  the  arrangement  of  the 
membrane  in  connection  with  the  latter  organ,  remain  for  con- 
sideration. 

Certain  complicated  adult  conditions,  encountered  in  this  part 
of  the  abdominal  cavity,  make  it  desirable  to  arrange  the  subject 
for  purposes  of  study  under  the  following  subdivisions  : 

I.  The  development  of  the  liver  and  of  its  vascular  system, 
and  the  significance  of  the  adult  circulation  of  the  liver  and  of 
the  foetal  remnants  connected  with  the  organ. 


DEVELOPMENT  OF  THE  LIVER.  141 

II.  The  anatomy  of  the  ventral  mesogastrium  and  the  changes 
produced  in  the  arrangement  of  the  membrane  by  the  develop- 
ment of  the  liver. 

I.  A;  Development  of  the  Liver — The  liver,  like  the  pancreas,  is 
developed  from  the  duodenum  as  an  outgrowth  from  the  hypo- 
blast lining  the  enteric  tube.  As  we  have  previously  noted,  the 
first  outgrowth  of  the  hepatic  diverticulum  is  closely  associated 
with  the  distal  pancreatic  outbud ;  in  fact  the  latter  arises  as  a 
derivative  from  the  hepatic  duct  rather  than  as  a  distinct  outbud 
from  the  intestinal  tube.  (This  close  association  of  the  hepatic 
duct  with  the  pancreas  is  well  seen  in  the  arrangement  of  the 
concealed  pancreas  of  some  teleosts  (cf  p.  117,  Fig.  196).) 

In  point  of  time  the  liver  is  the  first  accessory  structure  to 
develop  by  budding  from  the  primitive  alimentary  canal,  the 
pancreas  and  lung  following. 

In  the  primitive  type  of  development,  as  seen  in  Petromyzon 
and  in  the  Amphibia,  the  liver  appears  very  early,  as  a  divertic- 
ulum of  the  embryonic  intestinal  tube,  near  its  cephalic  ex- 
tremity, projecting  on  the  ventral  aspect  down  into  the  mass  of 
yolk-cells  (Fig.  237).  The  short  stretch  of  the  primitive  alimen- 
tary canal  cephalad  of  the  hepatic  diverticulum  corresponds  to 
the  foregut.  With  the  development  of  the  heart  the  primitive 
foregut  becomes  divided  into  pharynx  and  post-pharyngeal  seg- 
ment (oesophagus  and  stomach).  The  hepatic  diverticulum  then 
lies  immediately  dorsad  of  the  caudal  or  venous  extremity  of  the 
heart.  Hence  it  is  probable  that  the  liver  is  an  older  organ  in 
the  ancestral  history  of  the  vertebrates  than  the  pharynx  or  even 
the  heart.  The  liver  diverticulum  lies  in  close  connection  with 
the  omphalo-mesenteric  veins  which  return  the  blood  from  the 
yolk-sac  to  the  heart.  In  the  course  of  further  development,  as 
will  be  seen  below,  the  liver  comes  into  very  intimate  relations 
with  the  venous  circulation. 

In  human  embryos  of  3.2  mm.  the  primitive  hepatic  duct  ap- 
pears as  a  wide  hollow  pouch  composed  of  hypoblast  cells,  grow- 
ing between  the  two  layers  of  the  ventral  mesogastrium,  which 


142  ANATOMY  OF  THE  PERITONEUM. 

membrane,  extending  between  the  ventral  border  of  the  primitive 
stomach  and  the  ventral  abdominal  wall,  will  be  subsequently 
considered  in  detail.  The  liver,  in  developing  between  the  layers 
of  the  ventral  mesogastrium,  approaches  very  early  the  septum 
transversum  or  rudimentary  diaphragm  and  becomes  connected 
with  the  same.  A  mass  of  •  mesodermal  cells,  derived  from  the 
mesogastrium  and  from  the  primitive  mesodermal  intestinal 
wall  surrounding  the  hypoblastic  lining  of  the  tube,  covers  the 
csecal  termination  of  the  primitive  hepatic  duct,  forming  the  so- 
called  embryonic  hepatic  ridge.  This  mesodermal  tissue  accom- 
panies the  duct  in  its  further  growth  and  branching,  forming  the 
connective  tissue  envelope,  known  in  the  adult  as  the  capsule  of 
Glison.  The  primitive  hepatic  duct  is  directed  cephalad  in  the  me- 
sogastrium between  the  vitelline  duct  and  the  stomach  (Fig.  101). 

In  embryos  measuring  4,25  mm.  the  duct  is  0.24  mm.  long. 
Later  (in  embryos  of  8  mm.)  the  primitive  single  duct  divides 
into  two  secondary  branches,  indicating,  even  at  an  early  stage, 
the  adult  arrangement  of  the  duct,  as  formed  by  the  union  of  the 
right  and  left  hepatic  ducts  (Fig.  185). 

The  gall-bladder  in  embryos  of  this  size  (8  mm.)  is  a  well- 
defined  csecal  diverticulum,  branching  caudad  from  the  main 
hepatic  duct. 

The  vesicular  mucous  surface  is  thus  derived  from  the  enteric 
hypoblast  in  the  same  way  as  the  epithelial  lining  of  the  bile- 
ducts  and  capillaries.  The  external  muscular  and  fibrous  coats 
of  the  gall-bladder  are  developed  from  the  mesoderm  of  the 
mesogastrium. 

It  is  to  be  noted  that  at  an  early  stage  the  gall-bladder  is  de- 
rived from  the  main  duct  close  to  the  intestine,  the  latter  duct 
being  very  short.  Later  on  the  common  duct  grows  in  length, 
making  the  liver  more  and  more  a  gross  anatomical  organ  dis- 
tinct from  the  intestine.  The  cystic  duct  develops  as  the  result 
of  a  similar  increase  in  length  of  the  cystic  diverticulum.  The 
two  principal  secondary  branches  of  the  hepatic  duct  give  origin 
to  sprouts  or  buds.     These  are  derivatives  of  the  hypoblastic 


DEVELOPMENT  OF  THE  LIVER.  143 

cells  of  the  larger  ducts  and  may  from  the  beginning  be  hollow, 
possessing  a  lumen  continuous  with  that  of  the  parent  duct 
(Selachians,  Amphibians).  In  warm-blooded  animals  these 
sprouts  are  at  first  solid,  forming  the  s.  c.  hepatic  cylinders,  and 
only  subsequently  become  hollowed  out  with  the  further  devel- 
opment of  the  biliary  duct  system  of  the  liver.  The  rapid 
growth  of  the  organ  leads  to  a  great  increase  in  the  number  of  the 
hepatic  cylinders.  They  spread  out  on  all  sides,  finally  coalescing 
with  adjacent  buds  so  as  to  form  an  interlacing  network  whose 
meshes  are  filled  by  blood  vessels.  After  the  hepatic  cylinders 
have  become  canalized  they  preserve  the  same  arrangement, 
hence  the  resulting  biliary  capillaries  of  the  adult  form  an  anas- 
tomosing network.  Amphioxus  and  the  amphibians  have  a 
single  hepatic  outgrowth  (Fig.  49). 

In  the  Selachians  the  liver  arises  as  a  ventral  outgrowth  at 
the  hinder  end  of  the  foregut  immediately  in  front  of  the  vitelline 
duct,  thus  bringing  the  liver  from  the  beginning  into  close  prox- 
imity with  the  vitelline  veins  entering  the  heart.  Almost  as  soon 
as  formed  the  outgrowth  develops  two  lateral  diverticula,  open- 
ing into  a  median  canal.  The  two  diverticula  are  the  rudimentary 
lobes  of  the  liver  and  the  median  canal  uniting  them  is  the 
rudiment  of  the  common  bile-duct  and  gall-bladder. 

In  the  Teleosts  the  liver  arises  quite  late  (in  the  trout  about  the 
25th  day)  as  a  solid  outgrowth  from  the  intestinal  canal  close  to 
the  heart.  In  the  Amniota  the  liver  arises  in  the  same  position 
as  in  the  Anamnia,  but,  at  least  in  birds  and  mammals,  shows  its 
bifurcation  almost,  if  not  quite,  from  the  start.  The  two  forks 
embrace  between  them  the  omphalo-mesenteric  or  vitelline  veins 
just  before  the}'-  empty  into  the  sinus  venosus  of  the  heart. 

In  the  chick  the  liver  appears  between  the  56th  and  60th  hour, 
the  right  fork  being  always  of  greater  length  but  less  diameter 
than  the  left.  The  hepatic  outbud  in  the  rabbit  appears  during 
the  10th  day,  and  during  the  1 1th  day  begins  to  send  out  branches. 

In  man,  as  above  stated,  the  bud  appears  well  marked  in  em- 
bryos of  3  mm. 


144  ANAT03IY  OF  THE  PERITONEUM. 

[Certain  adult  variations  make  it  appear  possible  that  there  are 
two  human  embryonic  hepatic  buds,  a  cranial  and  a  caudal,  as  is 
the  case  in  birds.] 

I.  B.  Comparative  Anatomy  of  the  Liver. — The  liver,  phylogenet- 
ically  a  very  old  organ,  occurs  in  all  vertebrates,  for  the  csecal 
diverticulum  of  the  intestine  of  amphioxus  (Fig.  49)  has  prob- 
ably the  significance  of  a  hepatic  outbud. 

The  primitive  form  of  the  liver  is  symmetrically  bilobed,  a 
type  which  is  seen  well  in  the  chelonian  organ  (Fig.  238). 

In  size  the  liver  is  subject  to  great  variations.  It  is  usually 
larger  in  animals  whose  food  contains  much  fat.  Hence  carnivora 
in  general  have  a  larger  liver  than  herbivorous  animals. 

Its  shape  also  varies  considerably,  depending  on  the  form  of  the 
body  cavity  and  on  the  amount  and  disposition  of  the  available 
space.  Hence  in  the  snakes  the  organ  appears  long  drawn  out, 
flattened,  almost  ribbon-like  (Fig.  239),  while  the  relatively  very 
large  coronal  diameter  of  the  body  cavity  in  the  turtles  permits 
the  liver  to  expand  transversely  (Fig.  238). 

In  general,  when  the  liver  is  large  and  the  available  space  for  its 
reception  limited,  it  is  usually  split  into  several  (two  to  seven) 
lobes,  which  permit,  by  mutual  displacement,  the  accommodation 
of  the  organ  to  varying  space-conditions  of  the  body  cavity  (Fig. 
240).  Under  the  opposite  circumstances,  on  the  other  hand, 
even  the  primitive  bilobed  character  may  disappear  and  the  liver 
is  then  unlobed  (Fig.  241). 

The  presence  or  absence  of  a  gall-bladder  depends  appar- 
ently largely  on  the  character  of  the  food  and  on  the  habitual 
type  of  digestion.  In  many  vertebrates  digestion  is  carried  on 
nearly  continuously,  without  marked  interruption,  especially  in 
many  ungulates,  ruminants  and  rodents.  In  such  animals  the  gall- 
bladder is  absent.  It  is  also  absent  in  several  birds  (most  Parrots, 
Doves,  Ostrich,  Rhea  americana,  the  Cuculidse,  Rhamphastos, 
etc.).  This  variability  emphasizes  the  morphological  fact  that 
the  biliary  bladder  is  only  a  modified  portion  of  the  hepatic  duct 
system,  as  shown  by  the  development  above  outlined. 


PLATE    CXXI. 


SINUS   TER- 
MINALIS 


2D,  3D,  AND  4TH 
AORTIC  ARCHES 


VITELLINE 
VEINS 


R     VITELLINE  A 


POSTCAR- 
DINAL   V. 


L.   VITELLINE  A 


Fig.  247.— Diagram  of  the  circulation  of  the  yolk-sac  at  the  end  of  the  third  day  of  incuba- 
tion in  the  chick.  (After  Balfour.)  The  median  portion  of  the  first  aortic  arch  has  disappeared  ; 
but  its  proximal  end  forms  the  external,  its  distal  the  internal  carotid  arteries.  The  whole  blas- 
toderm has  been  removed  from  the  egg  and  is  viewed  from  below.  Hence  the  left  appears  on 
the  right,  and  vice  versa. 

Arteries  in  black. 

Veins  in  outline. 


L.   VITELLINE  V 


SINUS    VENOSUS 


R.   VITELLINE  V. 


YOLK-SAC  AND 
VITELLINE  CA- 
PILLARY NET- 
WORK 


Fig.  248. — Schema  of  vitelline  veins. 


PLATE    CXXII. 


SINUS    VENOSUS 


L     PRECAHDINAL   Y 


L.    DUCT    OF    CUVIER 
L.   POSTCARDINAL  V. 


VV.    HEPATIOE   REVEHENTES-C 

HEPATIC    CAPIL- 
LARY   SYSTEM 
L.    UMBILICAL    V. 

VV    HEPATICjE  advehentes-C 


L.  vitelline  v. 


UMBILICAL    VEIN     EN- 
TERING   UMBILICAL 
CORD     WITH      THE 
ARTERIES 


R.    PRECARDINAL   V. 
R.    DUCT    OF    CUVIER 


R      POSTCARDINAL    V. 
R.    UMBILICAL   V. 


R.    VITELLINE  CSUB- 
INTESTINAL)   V. 


UMBILICAL   OR    HYPO- 
'GASTRIC    ARTERIES 


Fig.  249.— Schema  of  umbilical  veins,  early  stage. 


L.    PRECARDINAL    V 


L.    DUCT  OF   CUVIER' 
L.    POSTCARDINAL   V 


HEPATIC    CAPIL 
LARY    SYSTEM- 


L.    UMBILICAL   V 


L.    VITELLINE    V 


R.    PRECARDINAL    V. 


R.    DUCT    OF    CUVIER 
R.    POSTCARDINAL  V. 


)-VV.   HEPATIC/E   REVEHENTES 


DUCTUS    VENOSUS 
R.    UMBILICAL   V. 


VV.    HEPATIC/E    ADVe- 
HENTES  'PRIMITIVE 
PORTAL   VEINS) 


TRANSV.  ANASTOMOSIS 
OF  VITELLINE  OR  OM- 
PHALO-MESENTERIC    VEINS 


L.    VITELLINE    V. 


Fig.  250. — Schema  of  primitiv'e  portal  circulation. 


PLATE    CXXIII. 


L.    PRECARDINAL  V.' 
L.   POSTCARDINAL  V 
L.    DUCT   OF   CUVIER 


L.    UMBILICAL   V 


COMMUNICATION      OF      L 

UMBILICAL  V.   WITH    INTRA 

HEPATIC      CAPILLARY     SYS 

TEM      BY    BRANCH     TO     LEFT' 

V.       HEPATICA      ADVEHENS 

AND    DUCTUS    VENOSUS 

DUODENUM 


OMPHALO- MESENTERIC 
(VITELLINE)    V. 


R.    PRECARDINAL    V. 


R.    POSTCARDINAL   V. 
R      DUCT    OF    CUVIER 


VV.    HEPATIOE    REVEHENTES 

R.    UMBILICAl^^.   _ 
DUCTUS    VENOSUS 
COMMUNICATION    OF 
R.   UMBILICAL  V.  WITH 
INTRAHEPATIC    CAPIL- 
LARY   SYSTEM 


VV.    HEPATIOE    ADVe- 
HENTES    (PORTAL    V.) 

1.    PROXIMAL    PERIDUODENAL 
ANNULAR    ANASTOMOSIS    OF 
OMPHALO- MESENTERIC 
(vitelline)    VEINS 


DISTAL    PERIDUODENAL 
ANNULAR   ANASTOMOSIS  OF 
OMPHALO -MESENTERIC 
(VITELLINE)    VEINS 

R.    OMPHALO-MESENTERIC 
(VITELLINE'    V. 


Fig.  251. — Schema  of  further  development  of  portal  circulation  and  connection  of 
same  with  umbilical  veins  in  early  stages. 


L.  PRECARDINAL  V 
L.  POSTCARDINAL  V 
L.    DUCT   OF   CUVIER. 


PROXIMAL    END    OF    L. 
UMBIt.lCAL    VEIN- 


INTERMEDIATE    SEGMENT 
OF      L.      UMBILICAL     VEIN 
TAKEN  INTO  HEPATIC  CIR- 
CULATION 


DISTAL    ENLARGED    SEG- 
MENT OF  L.    UMBILICALV. 
REDUCED    LEFT   HALF  OF 
PROXIMAL      ANNULAR 
ANASTOMOSIS     OF    OM- 
PHALO-MESENTERIC   V. 

PORTAL    VEIN 


PRECARDINAL   V. 

R.    POSTCARDINAL   V. 
R.    DUCT   OF   CUVIER 


PROXIMAL    END    RIGHT 
UMBILICAL   VEIN 
JVV.   HEPATIOE  REVEHENTES 


DUCTUS    VENOSUS 


RIGHT    UMBILICAL  V. 


ANASTOMOSIS  OF  R.  UM- 
BILICAL V.  WITH  INTRA- 
HEPATIC   CIRCULATION 

OBLITERATED    RIGHT    HALF 
OF   DISTAL  ANNULAR  ANAS- 

OMOSIS    OF   OMPHALO- 
MESENTERIC   V. 


DUODENU^ 


PORTAL    VEIN      FORMED    BY 
FUSION    OF    OMPHALO- 
MESENTERIC   VEINS 


Fig.  252. — Second  stage  in  development  of  circulation  through  portal  and  umbilical  veins. 
The  proximal  segment  of  the  main  portal  vein  is  formed  by  the  persistence  of  the  left  half  of  the 
distal  and  right  half  of  the  proximal  periduodenal  vascular  ring  of  the  omphalo-mesenteric  veins. 
The  distal  segment  of  the  main  jiortal  vein  is  the  product  of  the  fusion  of  the  omphalo-mesenteric 
veins,  and  becomes  connected  with  the  veins  of  the  intestinal  canal,  i)ancreas,  and  spleen.  The 
proximal  terminal  segment  of  both  umbilical  veins  becomes  included  in  the  system  of  the  ven?e 
hepaticse  revehentes. 


PLATE    CXXIV. 


LEFT    PRECARDINALV 
LEFT  POSTCARDINAL  V. 

LEFT  VEN/E  HEPATIC/E 
REVEHENTES,  INCLUD- 
ING PROXIMAL  SEG- 
MENT OF  LEFT  UMBILI- 
CAL   VEIN 


RIGHT    PRECARDINAL    V. 
RIGHT     POSTCARDINAL  V. 

RIGHT    DUCT   OF    CUVIER 

RIGHT    VEN£    HEPATlOe 
REVEHENTES,    INCLUD- 
ING   PROXIMAL  SEGMENT 
OF    RIGHT    UMBILICAL  V. 


m 


W4w 


...... .jw^mn, 

N    (LEFT    V.    HE-        \ 2i»* _,^^  ' 


LEFT    BR 
TAL   VEI 

PATICA    ADVEHENS) 

DISTAL      SEGMENT      OF 
LEFT    UMBILICAL   VEIN 


MAIN    TRUNK 
OF    PORTAL  V. 


DUODENUM 


-DUCTUS    VENOSUS 


OBLITERATED    INTER- 
MEDIATE     SEGMENT 
OF    RIGHT    UMBILICAL 
VEIN 


RIGHT  BRANCH  OF  POR- 
TAL VEIN  (RIGHT  V.  HE- 
PATICA  ADVEHENS) 
OBLITERATED  LEFT  HALF 
OF  PROXIMAL  PERIDUOD- 
ENAL   VASCULAR    RING 


OBLITERATED  RIGHT  HALF 
OF  DISTAL  PERIDUODENAL 
VASCULAR    RING 


DISTAL  SEGMENT  OF  RIGHT 
UMBILICAL  V.  ALMOST  EN- 
TIRELY        OBLITERATED 


Fig.  253.— Third  stage  in  development  of  jiortal  and  umbilical  veins  during  the  placental  period. 


ENTERIC   V. 


Fig.  254. — Corrosion  preparation  showing  cour.sc  of  jiortal  vein  and  tributaries  in  relation  to 
duodenum.     (Columbia  University  Museum,  No.  1857.) 


PLATE    CXXV. 


R     PRIMITIVE  JUGU- 
LAR VEIN  (PRECAR- 
DINAL) 


B.   DUCT  OF  CUVI  ER 


SINUS    VENOSUS 


R.    HEPATIC  V 


PORTAL   V.  — 


R.   UMBILICAL   V 


UMBILICAL    CORD 


L.    PRIMITIVE   JUGU- 
LAR   VEIN     (PRECAR- 
DINAL^ 
POSTCARDINAL  V. 


L.    DUCT   OF   CUVICR 

L.    HEPATIC    V. 

DUCTUS  VENOSUS 


L.    UMBILICAL   V. 


LOWER    EXTREMITY 


Fig.  255.— Human  embryo  of  10  mm.  cervico-coccygeal  measure.     Heart  and  ventral  body 
wall  removed  to  show  sinus  venosus  and  entering  veins.     (Kollmann,  after  His.) 


RIGHT   AURICLE 


LEFT    HEPATIC    VEIN- 


LEFT    BRANCH    OF 
PORTAL    VEIN 


UMBILICAL  VEIN 


1 V.    HEPATICA    COMMUNIS 


HEPATIC    SEGMENT 
OF    POSTCAVA 


RIGHT  HEPATIC    VEIN 


DUCTUS    VENOSUS 


IGHT    BRANCH  OF 
PORTAL   VEIN 


PORTAL   VEIN 


Fig.  25f).— Final  stage  of  development  of  portal  and  umbilical  veins  in  the  placental  period. 


PLATE   CXXVI. 


POSTCAVA 


L.    HEPATIC    V 


DUCTUS   VENOSUS' 


Fig.  257. — Schema  of  relation  of  postcava  to  hepatic  veins  and  ductus  venosus. 


POSTCAVA 

JUNCTION  OF  DUCTUS 
VENOSUS    AND    L.   HE- 
PATIC   VEIN 

L.    HEPATIC   V. 
DUCTUS    VENOSUS 


L.    BRANCH    PORTAL 

BRANCH   FR.   UMBI 

CAL  V.  TO   LEFT  LO 

INTRAHEPATIC     SE 

MENT  OF  UMBILICAL 

SUPPLYING      LEFT 

QUADRATE    LOB 

BRANCH   FROM    UMB 
ICAL  VEIN   TO    L.    LO 


R.    HEPATIC    V. 

R.    BRANCH    OF 
PORTAL   V. 


MAIN    TRUNK 
OF  PORTAL   V. 


BRANCH     FROM 
UMBILICAL    V. 
TO    QUADRATE 
LOBE 


Fig.  258.— Corrosion  preparation  of  venous  system  of  human  liver  in  foetus  at  term.   (Columbia 
University  Museum,  No.  1834.) 


POSTCAVA    WITH    OPENINGS    OF    HEPATIC    V. 


FALCIFORM    LIG.,    CON- 
TINUED     RIGHT      AND 
LEFT    INTO    CEPHALIC 
LAYER  OF  CORONARY 
LIGS. 

L.    TRIANGULAR   LIG 
FISSURE    FOR    DUC' 
TUS    VENOSUS 
SPIGELIAN   LOBE' 

TRANSV.   FISSURE 


LEFT    LOBE 


UMBILICAL 
VEIN 


VENTRAL   ABDOM- 
INAL  WALL' 


PORTION    OF 
DIAPHRAGM 


ADRENAL 
IMPRESSION 

R.  TRIANGULAR    LIG. 
POSTCAVA 
CAUDATE     LOBE 
PORTAL   VEIN 

R.    LOBE 
~-    -G ALL-BLADDER 

QUADRATE    LOBE 


UMBILICAL 
ARTERIES 

UMBILICAL 
CORD 


Fig.  259.— Injected  and  hardened  human  liver  from  foetus  at  term.     (Columbia  University 
Museum,  No.  1853.) 


PLATE    CXXVII. 


L.    HEPATIC   V, 


DUCTUS  VENOSUS 


BRANCHES  TO 
LEFT    LOBE 


R      HEPATIC   V 


PO^TCTIVA — 


L.    BRANCH    OF    POR- 
TAL V.  JOINING  RIGHT 
DIVISION    OF    UMBILI- 
CAL  VEIN 

RIGHT  BRANCH  OF 
PORTAL   VEIN 


PORTAL   VEIN 


BRANCH    TO    QUAD- 
RATE    LOBE 


UMBILICAL  VEIN 


Fig.  260. — Diagram  of  intrahepatic  fcetal  venous  circulation. 


L.   HEPATIC  VEINS 


OBLITERATED   DUC- 
TUS   VENOSUS 


LEFT   BRANCHES 
OF  PORTAL  VEIN 


OBLITERATED 
SEGMENT  OF 
UMBILICAL  V. 


POSTCAVA 


R     HEPATIC  VEIN 


RIGHT    BRANCH 
OF  PORTAL   VEiN 


PORTAL   VEIN 


BRANCH  TO  QUAD 
RATE   LOBE 


Fig.  261. — Diagram   illustrating  the  changes  in  the   intrahepatic   venous  circulation 
resulting  from  the  cessation  of  the  placental  circulation  at  birth. 


PLATE   CXXVIII. 


PRECARDINAL. 

(jugular'  V 


HEART 
DUCT  OF  CUVIER 
SUBCLAVIAN    V 


CARDINAL  SINUS 


LATERAL   VEIN 


GENITAL   VEINS 


ADVEHENT    RENAL- 
PORTAL  VEINS 


POSTCARDINAL  VEINS 


ADVEHENT    RENAL 
PORTAL     VEIN      DE- 
RIVED FROM  BIFUR- 
CATION  OF    CAUDAL 
VEIN 


VEINS  OF 
PELVIC   FIN 


CAUDAL   VEIN 


INF.    JUGULAR    VEIN 


HEPATIC    SINUS 


HEPATIC    POR- 
TAL  VEIN 

.CESOPHAGEAL  VEIN 


STOMACH    AND 
GASTRIC  VEINS 


REVEHENT    RENAL- 
PORTAL    VEINS 


MID-GUT    AND    IN- 
TESTINAL   VEINS 


LATERAL  VEIN 


PERICLOACAL 
NETWORK 


CUTANEOUS    VEIN 
OF  TAIL 


Fig.  262. — Diagram  of  the  veins  of  a  selacliian.     (Wiedersbeini,  after  Parker.) 

The  lateral  vein  arises  from  a  venous  network  surrounding  the  cloaca,  receiving  one  or  more 
cutaneous  veins  of  the  tail,  veins  of  the  body-wall,  and  veins  of  the  pelvic  fins. 

The  caudal  vein  divides  at  the  posterior  end  of  the  kidney  into  the  two  renal-portal  veins, 
from  which  the  advehent  veins  of  the  renal-portal  system  are  derived.  The  revehent  renal-por- 
tal veins  join  to  form  the  posterior  cardinal  veins,  which,  after  dilating  enormously  to  form  the 
cardinal  sinuses,  join  with  the  anterior  jugular,  subclavian,  and  lateral  veins  to  form  the  ducts  of 
Cuvier.  The  latter  receive  the  inferior  jugular  veins,  from  the  deep  parts  of  the  head  and  neck 
and  the  terminations  of  the  hepatic  portal  system  (hepatic  sinus). 

The  hepatic  portal  vein  is  formed  by  the  veins  of  the  oesophagus,  stomach,  and  intestines. 
After  traversing  the  capillary  vessels  of  the  liver,  the  revehent  hepatic  veins  unite  to  form  an 
extensive  hepatic  sinus  before  entering  the  heart. 


m 


COMPARATIVE  ANATOMY  OF  LIVER.  145 

A  great  variety  is  observed  in  the  arrangement  of  the  biliary 
ducts,  through  which,  at  the  period  of  intestinal  digestion,  bile 
passes  from  the  liver  and  gall-bladder  into  the  intestine,  while  in 
the  intervals  of  digestion  the  secretion  is  only  carried  from  the 
liver  to  the  bladder.  The  following  main  types  of  the  biliary 
duct  system  may  be  recognized : 

1.  The  hepatic  duct  joins  the  cystic  to  form  the  common  bile- 
duct,  entering  the  duodenum  by  passing  obliquely  through  the 
intestinal  wall  (Fig.  242).  This  form  is  encountered  in  man 
and  in  most  mammals.  It  is  also  found  in  some  birds  {Buceros), 
many  amphibians,  and  in  some  fish  {Lophius).  Instead  of  one 
hepatic  duct  two  may  join  the  cystic  duct  separately  to  form  the 
common  bile  duct  (Phoca  litorea),  or  the  number  of  hepatic  ducts 
may  be  further  increased.  The  separate  hepatic  ducts  then 
unite  successively  with  the  cystic  duct.  This  occurs  in  many 
mammals  ( as  Tardus,  Galeopithecus,  monotremes)  and  in  some 
fishes  {Xiphias,  Trigla,  Accipenser)  (Fig.  243). 

2.  Of  two  hepatic  ducts  only  one  helps  to  form  with  the  cystic 
duct  the  common  duct,  while  the  other  leads  from  the  liver  trans- 
versely into  the  bladder,  especially  into  the  neck,  forming  the 
hepatico-cystic  duct  (Fig.  244).  This  arrangement  is  found  in 
several  mammals  (calf,  sheep,  dog). 

3.  No  common  bile-duct  is  formed.  The  hepatic  and  cystic 
ducts  each  empty  separately  into  the  intestine  (hepato-enteric  and 
cysto-enteric  ducts),  while  a  hepato-cystic  duct  carries  the  bile 
directly  from  the  liver  to  the  gall-bladder  (Fig.  245). 

Lnitra  vulgaris  among  mammalia,  the  majority  of  the  birds  and 
several  reptilia  present  this  type. 

When  the  gall-bladder  is  absent  a  single  large  hepato-enteric 
duct  is  found,  or  instead  a  number  of  smaller  ducts  which  enter 
the  intestine  successively. 

I.  C.  Development  of  Vascular  System  of  Liver. — In  order  to  com- 
prehend the  peritoneal  relations  of  the  adult  liver  it  is  absolutely 
necessary  to  have  a  clear  understanding  of  the  development  of 
the  vascular  system  in  connection  with  the  gland. 

10 


146  ANATOMY  OF  THE  PERITONEUM. 

For  our  purpose,  in  the  first  place,  a  serial  consideration  of  the 
successive  stages,  illustrated  by  schematic  diagrams,  will  prove 
most  practicable.  These  diagrams  represent  the  structures  in  the 
dorsal  view,  i.  e.,  in  the  position  which  they  would  occupy  in  the 
adult  liver  with  the  gland  resting  on  its  upper  or  convex  surface 
and  with  the  ventral  sharp  margin  turned  toward  the  beholder 
(see  Fig.  259). 

The  development  of  the  venous  system,  especially  in  connection 
with  the  liver,  presents  a  somewhat  complicated  series  of  succes- 
sive conditions.  After  having  become  familiar  with  the  principal 
typical  embryonal  stages,  as  shown  in  the  following  diagrams, 
the  student  is  strongly  recommended  to  cement  this  knowledge 
by  the  comparative  examination  of  the  venous  system.  The  per- 
manent veins  of  the  lower  vertebrates,  while  in  many  cases  not 
strictly  homologous  to  those  of  the  higher  forms,  yet  are  excellent 
objects  for  study,  since  they  serve  to  illustrate  temporary  stages  in 
the  development  of  the  mammalian  venous  system,  and  to  that 
extent  are  of  aid  in  comprehending  one  of  the  most  difiicult  and 
important  chapters  in  human  anatomy.  At  the  conclusion  of  the 
diagrammatic  consideration  of  the  mammalian  development  a 
number  of  comparative  facts  will  be  put  together  for  this 
purpose. 

1.  Early  Stage. — In  the  earlier  developmental  stages  in  mamma- 
lian embryos  the  primitive  dorsal  aorta  extends  caudad  along  the 
ventral  aspect  of  the  vertebral  axis,  giving  off  paired  vitelline  or 
omphalo-mesenteric  arteries  to  the  yolk-sac  and  allantoic  arteries 
to  the  embryonic  urinary  bladder  or  allantois  (Figs.  246  and  247). 

The  blood  is  returned  from  the  vascular  area  of  the  yolk-sac  by 
two  vitelline  or  omphalo-mesenteric  veins,  which  unite  near  the 
heart  to  form  a  common  trunk,  continued  as  the  sinus  venosus  into 
the  caudal  or  auricular  extremity  (venous  end)  of  the  primitive 
tubular  heart  (Figs.  246,  247  and  248). 

2.  Development  of  Allantois.  Stage  of  Placental  Circulation. — The  pla- 
cental circulation,  replacing  the  temporary  vitelline  circulation 
of  the  earliest  stages,  is  inaugurated  by  the  appearance  of  two 


DEVELOPMENT  OF  HEPATIC  VASCULAR  SYSTEM.  147 

umbilical  veins,  which  pass  cephalad,  imbedded  in  the  tissue  of 
the  ventral  mesogastrium,  to  empty  into  the  sinus  venosus  near 
the  vitelline  veins  (Fig.  249).  The  umbilical  veins  return  the 
oxygenated  blood  from  the  placenta  to  the  embryo.  At  first  the 
right  umbilical  vein  is  the  larger  of  the  two. 

The  sinus  venosus  at  this  time  also  receives  two  large  veins, 
transversely  directed,  called  the  ducts  of  Cuvier,  which  are  formed 
near  the  heart  by  the  union  of  the  anterior  cardinal  (primitive 
jugular)  and  posterior  cardinal  veins,  draining  respectively  the 
head  end  of  the  embryo,  and  the  body  walls  and  Wolffian  bodies. 

The  vitelline  veins  are  placed  on  each  side  of  the  primitive 
small  intestine,  and  become  connected  with  each  other  by  a  broad 
anastomotic  branch  (Fig.  249).  When  the  hepatic  outgrowth  buds 
from  the  duodenum  the  vitelline  veins  send  out  branches  which 
break  up  into  a  wide-meshed  capillary  network  in  the  mesodermic 
tissue  enveloping  the  hepatic  cylinders.  Hence  at  this  period 
the  circulation  in  the  vitelline  veins  is  made  up  of  three  districts  : 

(a)  Distal  segment  of  veins,  coursing  along  duodenum,  and 
joined  by  a  transverse  anastomosis,  before  reaching  the  liver  bud 
(subintestinal  veins). 

(6)  Middle  segment,  from  which  capillary  vessels  are  derived, 
ramifying  upon  and  between  the  developing  hepatic  cylinders. 

(c)  Proximal  segment,  formed  by  the  continuation  of  the  prox- 
imal part  of  the  vitelline  veins  into  the  sinus  venosus  of  the  heart. 

3.  Formation  of  Portal  Circulation.  A. — With  the  further  develop- 
ment of  the  liver  the  direct  connection  of  the  distal  segment  of 
the  vitelline  veins  with  the  sinus  venosus  becomes  lost,  the  in- 
termediate segment  being  entirely  broken  up  into  an  intrahepatic 
network  (Fig.  250).  Hence  all  the  blood  brought  to  the  liver 
by  the  vitelline  veins  (vense  hepaticse  advehentes)  passes  through 
the  hepatic  capillary  circulation,  before  it  is  carried  by  the  proxi- 
mal segment  of  the  vitelline  veins  (venae  hepaticse  revehentes) 
into  the  sinus  venosus.  The  amount  of  this  blood  increases  with 
new  connections  which  the  vitelline  veins  make  with  the  venous 
radicles  developing  in  the  intestinal  tract   and  its  appendages. 


148  ANATOMY  OF  THE  PERITONEUM. 

In  proportion  as,  with  the  development  of  the  placenta  and  re- 
duction of  the  yolk-sac,  the  original  significance  of  the  vitelline 
veins  as  nutritive  and  respiratory  vessels  disappears,  this  second- 
ary connection  of  the  vitelline  veins  with  the  veins  of  the  ali- 
mentary tract  becomes  more  and  more  important,  until  finally 
the  original  vitelline  veins,  now  properly  called  omphalo-mesen- 
teric  veins,  return  the  blood  from  the  intestinal  tube,  pancreas 
and  spleen  to  the  liver. 

The  vense  hepaticse  advehentes,  becoming  connected  in  this 
way  with  the  developing  intestine,  pancreas  and  spleen,  form  the 
rudiments  of  the  future  portal  system,  while  the  venae  hepaticse 
revehentes  are  prototypes  of  the  hepatic  veins  of  the  adult  circu- 
lation. 

B.  Development  of  the  Portal  Vein. — The  distal  subintestinal  seg- 
ments of  the  vitelline  veins  are  early  united  by  a  transverse  anas- 
tomotic branch.  The  section  of  the  veins  above  this  anastomosis 
is  seen  already  in  Fig.  250  to  have  assumed  an  annular  shape, 
while  the  veins  below  the  primary  anastomosis  are  approaching 
each  other  to  form  a  second  ring-like  junction. 

In  Fig.  251  the  subintestinal  segments  of  the  two  vitelline  veins 
are  seen  to  have  communicated  with  each  other  by  transverse 
anastomotic  branches  around  the  duodenum,  two  of  these 
branches  being  situated  ventrad  and  one  dorsad  of  the  intestinal 
tube.  These  branches,  and  the  portions  of  the  primitive  vitelline 
veins  between  their  points  of  derivation,  form  two  vascular  loops 
or  rings,  encircling  the  primitive  duodenum  (Fig.  251). 

The  distal  portions  of  the  vitelline  veins,  before  reaching  the 
caudal  annular  duodenal  anastomosis,  next  fuse  into  a  single  lon- 
gitudinal vessel  which  also  receives  the  veins  from  the  stomach, 
intestine,  spleen,  and  pancreas,  and  forms  the  beginning  of  the 
portal  vein. 

By  atrophy  of  the  right  half  of  the  lower,  and  of  the  left  half 
of  the  upper  duodenal  venous  ring  (Figs.  252  and  253),  the  proxi- 
mal portion  of  the  portal  vein  is  formed  as  a  single  vessel,  taking 
a  spiral  course  around  the  duodenum  (Fig.  256).     Hence  in  the 


FINAL  ARRANGEMENT  OF  THE  UMBILICAL    VEINS.  149 

adult  the  portal  vein  and  its  principal  branch  (the  superior  mesen- 
teric vein)  crosses  over  the  ventral  Surface  of  the  duodenum  (third 
portion),  turns  along  the  mesal  side  of  the  second  portion,  and 
then  continues  to  the  liver  along  the  dorsal  aspect  of  the  first 
portion  (Fig.  254).  Note — In  comparing  Fig.  254  with  the  sche- 
matic figures  it  should  be  noted  that  the  same  presents  the  parts 
in  the  ventral  view,  while  the  schemata  offer  the  dorsal  aspect. 

4.  Changes  Leading  to  the  Final  Arrangement  of  the  Umbilical  Veins. — A 
very  important  rearrangement  of  the  umbilical  veins  takes  place. 
These  veins  originally  course  in  the  lateral  abdominal  wall,  close 
to  the  fold  of  the  amnion  (Fig.  255),  and  then  turn  cephalad  of 
the  developing  liver  along  the  septum  transversum  to  empty  into 
the  sinus  venosus  at  each  end  (Figs.  249  and  250).  The  right 
umbilical  vein  is  at  first  the  larger. 

This  symmetrical  arrangement,  and  the  direct  connection  of  the 
umbilical  veins  with  the  sinus  venosus,  now  becomes  lost  by  the 
occurrence  of  the  following  changes : 

1.  At  first  (Fig.  249)  all  the  blood  carried  to  the  liver  by  the 
omphalo-mesenteric  veins  passes  through  the  hepatic  capillary 
network  before  being  conducted  by  the  venae  revehentes  to  the 
sinus  venosus.  Very  early,  however,  a  new  intrahepatic  channel 
develops,  the  ductus  venosus  (Figs.  250-253),  which  passes  ob- 
liquely between  the  entrance  of  the  left  omphalo-mesenteric  vein 
into  the  capillary  system  (1.  v.  advehens)  and  the  termination  of 
the  right  omphalo-mesenteric  vein  (r.  vena  revehens)  in  the  sinus 
venosus. 

In  human  embryos  of  4  mm.  the  ductus  venosus  can  already 
be  distinguished,  and  in  embryos  of  5  mm.  the  vessel  has  assumed 
considerable  proportions. 

2.  A  communication  is  next  established  on  both  sides  between 
the  capillary  hepatic  network  in  the  portion  of  the  Uver  nearest 
to  the  abdominal  wall  and  the  umbilical  veins  as  they  ascend 
imbedded  in  the  abdominal  wall  (Fig.  251). 

This  connection  is  usually  from  the  start  larger  on  the  left  side 
and  connects  with  the  left  omphalo-mesenteric  vein  just  at  the 


150  ANATOMY  OF  THE  PERITONEUM. 

point  where  the  same  is  about  to  be  continued  into  the  ductus 
venosus.  This  connection  becomes  rapidly  larger,  so  that  the 
ductus  venosus,  which  at  first  appeared  merely  as  an  anastomotic 
channel  between  the  left  omphalo-mesenteric  vein  and  the  termi- 
nal portion  of  the  right  omphalo-mesenteric  vein,  now  forms  the 
main  continuation  of  the  left  umbilical  vein.  This  vessel  grows 
very  rapidly  up  to  its  connection  with  the  ductus  venosus  and 
soon  exceeds  the  right  umbilical  vein  in  size  (Fig.  252).  Beyond 
the  ductus  venosus  on  the  other  hand  the  proximal  segment  of 
the  left  umbilical  vein  diminishes  in  size,  and  loses  its  indepen- 
dent character  by  incorporation  in  the  hepatic  circulation.  Only 
its  terminal  portion,  emptying  into  the  sinus  venosus,  is  pre- 
served. This  is  surrounded  by  the  growing  masses  of  hepatic 
cylinders  and  is  converted  into  a  vena  revehens. 

The  connection  of  the  right  umbilical  vein  with  the  liver  ves- 
sels is  at  first  symmetrical  to  that  on  the  left  side,  but  less 
strongly  developed.  The  effect  of  this  connection  is  to  reduce 
in  the  same  way  the  proximal  segment  of  the  right  umbilical 
vein  and  to  convert  its  termination  into  a  vena  revehens.  With 
the  great  development  of  the  left  vein,  however,  the  vein  on  the 
right  side  gradually  diminishes  and  finally  loses  its  connection 
with  the  intrahepatic  circulation  altogether.  The  right  umbil- 
ical vein  is  now  reduced  to  a  vessel  of  the  ventral  abdominal  wall, 
which  carries  blood  in  the  reverse  of  the  original  direction,  i.  e., 
from  the  abdominal  wall  caudad  into  the  left  umbilical  vein 
(Figs.  253  and  255). 

The  connection  thus  established  between  the  umbiHcal  vein 
and  the  portal  circulation  results  in  the  formation  of  a  single 
large  (the  original  left)  umbilical  vein  which,  throughout  the 
remainder  of  foetal  life,  returns  all  of  the  placental  blood  (Fig. 
253). 

The  newly  developed  hepatic  portion  of  the  left  umbilical  vein 
becomes,  however,  not  only  connected  with  the  ductus  venosus, 
but  also  with  the  right  part  of  the  upper  venous  ring,  derived 
from  the   right  omphalo-mesenteric  vein  (Fig.  253).     This  con- 


FINAL  ARRANGEMENT  OF  THE  UMBILICAL    VEINS.  151 

nection  forms  the  left  portal  vein  of  the  adult,  and  enlarges 
rapidly. 

The  terminations  of  the  ductus  venosus  and  of  the^vense  he- 
paticse  revehentes  undergo  a  number  of  secondary  changes  in 
relative  position.  The  left  hepatic  vein  loses  its  direct  connec- 
tion with  the  sinus  venosus,  and  now  opens  into  the  termination 
of  the  ductus  venosus,  into  which  the  right  hepatic  vein  also 
empties.  This  common  vessel  (v.  hepatica  communis)  subse- 
quently forms  the  proximal  segment  of  the  postcava  when  this 
vessel  develops  (Fig.  256). 

The  blood,  therefore,  returned  to  the  liver  by  the  left  umbilical 
vein  divides  at  the  transverse  fissure  into  three  streams.  Two  of 
these  pass  through  the  connection  with  the  portal  vein  and  through 
branches  developed  from  the  hepatic  part  of  the  umbilical  vein 
into  the  capillary  system  of  the  right  and  left  lobe.  The  third 
continues  through  the  ductus  venosus  to  the  common  hepatic  vein 
and  sinus  venosus  (Fig.  256).  The  ductus  venosus  thus  becomes 
the  chief  vessel  returning  arterialized  placental  blood  to  the  heart. 
When  the  postcava  develops  fully  the  hepatic  segment  of  this 
vessel  also  joins  the  terminal  part  of  the  ductus  venosus  (Fig. 
256)  and  gradually  replaces  the  same  as  the  main  returning 
venous  channel,  the  proximal  part  of  the  ductus  venosus  being 
incorporated  in  the  vena  cava  (Fig.  257).  The  postcava  then 
receives  the  right  hepatic  veins  separately,  while  the  left  hepatic 
veins  and  ductus  venosus  open  together  into  the  main  vein.  This 
condition  obtains  up  to  the  time  of  birth  and  the  consequent 
interruption  of  the  placental  circulation. 

While  at  first  the  ductus  venosus  communicates  throughout  its 
entire  length  with  the  meshwork  of  the  hepatic  capillary  system, 
a  separation  into  two  segments,  i.  e.,  ductus  venosus  proper  and 
intrahepatic  segment  of  umbilical  vein,  is  established  after  the  free 
communication  with  the  left  umbilical  vein  takes  place.  This 
condition  is  exhibited  in  Fig.  258,  which  represents  the  corroded 
venous  system  of  the  foetal  liver,  and  in  Fig.  259,  showing  an 
injected  liver  in  the  fcetus  at  term. 


152  ANATOMY  OF  THE  PERITONEUM. 

It  will  be  observed  that  the  umbilical  vein  on  entering  the  liver 
gives  off  a  large  branch  to  the  left  lobe,  and  a  smaller  branch  on 
the  right  side  to  the  quadrate  lobe,  which  act  as  the  main  vense 
advehentes  of  these  portions  of  the  liver.  Arrived  at  the  trans- 
verse fissure  the  umbilical  vein  divides  into  three  branches,  at 
right  angles  to  each  other.  The  left  branch  enters  the  left  lobe, 
the  right  branch  becomes  directly  continuous  with  the  left  main 
division  of  the  portal  vein,  while  the  central  branch,  continuing 
the  direction  of  the  umbilical  vein,  passes  dorsad,  as  the  ductus 
venosus  proper,  to  join  the  left  hepatic  vein  close  to  its  entrance 
into  the  postcava. 

5 .  Changes  Conseqiuent  upon  tlie  Establishment  of  Pulmonary  Respiration. — 
After  birth  the  umbilical  vein  and  its  continuation,  the  ductus- 
venosus,  become  obliterated,  the  former  constituting  the  round 
ligament  of  the  liver,  the  latter  the  ligament  of  the  ductus  venosus, 
both  structures  imbedded  in  corresponding  portions  of  the  sagit- 
tal fissure  on  the  caudal  and  dorsal  surfaces  of  the  adult  liver 
(Figs.  284  and  286).  The  lateral  branches  of  the  umbilical  vein, 
however,  in  its  course  from  the  ventral  margin  of  the  liver  to  the 
transverse  fissure  (Fig.  258),  remain  pervious  and  are  transferred 
to  the  portal  circulation. 

It  will  be  noticed,  in  reference  to  the  direction  of  the  blood  cur- 
rent, that  at  birth  a  sudden  reversal  takes  place  in  the  right  ter- 
minal branch  of  the  umbilical  vein  at  the  transverse  fissure  (Figs. 
260  and  261).  Before  birth  the  blood  current  of  the  umbilical 
vein  divides  into  three  streams,  right,  left  and  central.  The  latter 
enters  the  ductus  venosus.  The  left  enters  the  liver  directly,  the 
right  traverses,  from  left  to  right,  the  segment  between  the  ter- 
mination of  the  umbilical  and  the  bifurcation  of  the  portal  vein. 
This  segment  in  the  adult  carries  blood  from  right  to  left,  as  left 
branch  of  the  portal  vein.  In  the  foetus,  however,  the  blood 
traverses  this  segment  from  left  to  right,  in  passing  from  the 
umbilical  to  the  right  branch  of  the  portal  vein.  The  blood 
entering  the  liver  through  the  portal  vein  passes  chiefly  into  the 
right  division  of  that  vessel  (Fig.  260). 


PLATE    CXXIX. 


PRECAROINAL 

(jugularI  V 


SUBCLAVIAN    V. 


HEPATIC    VEIN 


PROXIMAL    SEGMENT 
OF   POSTCAVA 


postcaroinal 
(azygos)  vein 


VEINS      FROM 
CLOACA,    BLAD- 
DER,  AND   END- 
GUT 

DISTAL   SEGMENT 
OF    POSTCAVA 

HEVEHENT    RENAL- 
PORTAL   VEINS 


DUCT  OF  CUVIER 


NTESTINE 


HEPATIC    POR- 
TAL  SYSTEM 


HEPATIC  PORTAL  V. 


ABDOMINAL   VEIN 


ADVEHENT    RENAL- 
AORTAL   VEIN 


ILIAC    VEIN 


CAUDAL  VEIN 


Fig.  263. — Diagram  of  the  veins  of  urodele  amphibian  {Salamandra  maculosa).  (Wiedersheim.) 

The  caudal  vein  bifurcates  at  the  posterior  extremity  of  the  kidneys  to  form  the  afferent 
trunks  of  the  renal-portal  system  along  the  lateral  border  of  the  kidneys,  from  which  the  adve- 
hent  veins  of  the  renal-portal  system  are  derived.  The  iliac  or  femoral  vein  divides  into  an 
anterior  and  a  posterior  branch,  the  latter  opening  into  the  afferent  renal-portal  vein,  while  the 
former,  uniting  with  the  one  of  the  opposite  side,  forms  the  abdominal  vein,  and  receives  vessels 
from  the  bladder,  cloaca,  and  end-gut.  The  revehent  veins  of  the  renal-portal  system,  emerging 
upon  the  ventral  surface  of  the  kidneys,  empty  into  a  single  median  vessel,  the  distal  or  renal 
section  of  the  postcava  or  vena  cava  inferior.  Proceeding  cephalad,  the  proximal  or  hepatic  sec- 
tion of  this  vessel,  after  traversing  the  liver  and  receiving  the  revehent  hepatic  veins  of  the 
hepatic  portal  system,  empties  into  the  sinus  venosus  of  the  heart.  Previous  to  entering  the  liver 
the  postcava  gives  off  the  two  posterior  cardinal  or  azygos  veins,  which  continue  cephalad,  receiv- 
ing tributary  segmental  veins  from  the  body-walls  and  reach  the  sinus  venosus  by  joining  the 
subclavian  veins.  These  latter  uniting  with  the  anterior  cardinal  (jugular)  veins  form  the  ducts 
of  Cuvier  (precaval  veins). 

The  abdominal  vein  continues  cephalad  in  the  ventral  mesogastrium  to  the  liver,  giving  off  a 
number  of  smaller  branches,  which  enter  the  hepatic  i)ortal  circulation  by  penetrating  the  ventral 
surface  of  the  liver  between  the  layers  of  the  ventral  mesogastrium,  while  the  main  continuation 
of  the  vessel  joins  the  hepatic  portal  vein  at  its  point  of  entrance  into  the  liver. 

The  hepatic  portal  vein  is  formed  by  tributaries  returning  the  blood  from  the  digestive  tract 
(intestinal  canal,  spleen,  pancreas).  The  blood,  after  traversing  the  hepatic  portal  circulation,  is 
conducted  by  the  hepatic  revehent  veins  to  the  proximal  section  of  the  postcava.  A  number  of 
secondary  or  accessory  portal  veins  pass  from  the  anterior  portion  of  the  intestinal  canal  (oesoph- 
agus, stomach)  directly  to  the  liver. 


PLATE    CXXX. 


I    i    /^9. 


ABDOMINAL   VEIN 

JOINING    HEPATIC 

PORTAL  VEIN 


ABDOMINAL  VEIN 


STOMACH     DIS- 
PLACED   CAUDAD 


^^"^    (azygos)  veins 


POSTCAVAL  VEIN 


PANCREAS 


EPATIC    PORTAL  V. 


KIDNEY 

INTERRENAL   SEG- 
MENT OF  POSTCAVA 
ILIAC   VEIN 


Fig.  264.— Dissection  of  veins  of  Xecturus  maculatus,  mud-puppy.  (Columbia  University 
Museum,  No.  1835.) 

The  postcava  has  been  divided  at  the  cephalic  end  of  the  liver  just  before  entering  the  sinus 
venosus,  and  the  postcardinals  have  been  cut  prior  to  their  junction  with  the  subclavian  veins. 

The  stomach  has  been  turned  caudad.  The  abdominal  vein  has  been  divided  after  the  com- 
mon trunk  has  been  formed  by  branches  from  the  iliac  veins.  The  latter  are  seen  entering  the 
afferent  renal-portal  vein,  derived  from  the  bifurcation  of  the  caudal  vein,  along  the  lateral 
border  of  the  kidneys. 

The  junction  of  the  main  trunk  of  the  abdominal  vein  with  the  hepatic  portal  vein  takes 
place  close  to  the  liver  under  cover  of  the  pancreas.  A  series  of  accessory  portal  veins  continuous 
with  the  abdominal  vein  enter  the  ventral  surface  of  the  liver  between  the  layers  of  the  ventral 
mesogastrium.  The  inter-renal  segment  of  the  postcava  receives  the  revehent  renal-portal  veins. 
The  iliac  vein  enters  the  advehent  renal-portal  veins  derived  from  the  caudal  vein. 


PLATE    CXXXI. 


PULMONARY    V 
CUTANEOUS    V. 


CARDIAC    V. 


KIDNEY,  WITH   REVE 
HENT    RENAL-PORTAL 
VEINS    EMPTYING    INTO 
POSTCAVA 

ABDOMINAL   V. 


EXT.    JUGULAR    V. 
BRACHIO-CEPH.    V. 

SUBCLAV.  V. 
SINUS    VENOSUS 

POSTCAVA 
HEPATIC    V. 

PORTAL  V. 
INTESTINE 


f ADVEHENT    RENAL- 
l PORTAL   VEINS 


SCIATIC    VEIN 
FEMORAL   VEIN 


Fig.  265. — Venous  system  of  Rana  esculenta,  frog.     (Ecker.) 


PLATE    CXXXII. 


R.    INT.    JUGULAR    V. 
(PRECARDINAL   V.) 


R.    AORTIC    ARCH    WITH 
CAROTID    TRUNK 

R.    AURICLE 

R.    SUBCLAVIAN  A. 

PROXIMAL  SEGMENT  OF 
POSTCAVA  ENTERING 
RIGHT    AURICLE 


VERTEBRAL  (AZYGOS) V. 
COMMUNICATING     WITH 
INTRAHEPATIC       SEG- 
MENT  OF    POSTCAVA 


POSTCAVA    DIVIDED    AT 
ENTRANCE    INTO    LIVER 


ABDOMINAL   VEIN 


DIVISION  OF  ABDOMI- 
NAL V.  ON  bladder' 


DIVIDED    ENDS    OF 

RIGHT    BRANCH    OF 

ABDOMINAL    VEIN 


AFFERENT   RENAL-PORTAL 

V.    FROM    ABDOMINAL   V. 

END-GUT 

RIGHT    PENIS    EVERTED 


EXT.    JUGULAR    V. 


L.     INT.    JUGULAR    V 

(PRECARDINAL    V.) 

AORTIC    ARCH 


-^— L.    SUBCLAVIAN    V, 

VERTEBRAL    (aZYGOS^    V 
JOINING  SUBCLAVIAN    V 


PULMONARY    A. 
VENTRICLE 


POSTCARDINAL 
ANASTOMOSIS 


L.    POSTCARDINAL    V. 
VAS    DEFERENS 


AFFERENT  RENAL- POR- 
TAL   V.    FROM    ABDOMI- 
NAL   VEIN 
LEFT    KIDNEY 


UROGENITAL   ORIFICES 
IN    DORSAL    WALL 
OF    CLOACA 


Fig.  266. — Systemic  veins  of  Ljuana  tnbercnlata.  The  alimentary  canal  and  appendages, 
together  with  the  hepatic  portal  vein  and  the  intrahepatic  segment  of  the  postcava,  have  been 
removed.  The  liver  occupies  the  space  between  the  divided  ends  of  the  postcava.  The  vertebral 
vein  represents  tln'  rudimentary  proximal  segment  of  the  postcardinal  vein  corresponding  to  the 
mammalian  azygos  vein.     (Columbia  University  Museum,  No.  1.320.) 


PLATE    CXXXIII. 


AORTA 

R.  AORTIC  ARCH  WITH 

CAROTID  TRUNK 

SINUS  VCNOSUS 

L  AORTIC  ARCH 
R.  AORTIC  ARCH  WITH 
SUBCLAVIAN  ARTERIES 

POSTCAVA- 


VERTEBRAL  (aZYGOS^ 
V.  CONNECTING  WITH 
INTRAHEPATIC  SEG- 
MENT   OF     POSTCAVA 


EXT.  JUGULAR  V. 

.NT.  JUGULAR 
iPRECARDINALJ  V. 

PULMONARY  A. 

L.  AORTIC  ARCH 

L.  SUBCLAVIAN  V 

L  SUBCLAV.AN  A. 
L.  VERTEBRAL 

(azygos)  V. 


VERTEBRAL   (aZY- 
GOS)    VEINS 


Fig.  267. — Veins  of  Iguana  tnberculata.  Connection  of  systemic  veins  with  sinus  venosus  of 
heart.  The  rudimentary  system  of  the  vertebral  (azygos)  veins  and  their  proximal  connection 
with  the  subclavian  vein  are  shown.     (Columbia  University  Museum,  No.  1859.) 


ABDOMINAL  V 
HEPATIC  PORTAL  V 


POSTCAVA    ENTERING 
SINUS    VENOSUS 


POSTCAVA    ENTER- 
ING   LIVER 


Fig.  2(^. — Corrosion  preparation  of  venous  system  of  liver  in  Iguana  tubereulata.  The  hepatic 
portal  system  and  its  connection  with  the  abdominal  vein,  as  well  as  the  relation  to  the  postcava, 
are  shown.  The  preparation  supplements  Fig.  266,  showing  the  parts  which  have  been  removed 
in  the  latter.     (Columbia  University  Museum,  No.  1860.) 


PLATE    CXXXIV. 


POSTCAVA    DI- 
VIDED   AT    EN- 
TRANCE   INTO 
LIVER 


TRANSV.  ANASTOMO- 
SIS   BETW. POSTCAR- 
DINAL    VEINS 

L.   POSTCARDINAL  V 


L      DIVISION    OF 

ABDOMINAL    V. 

BLADDER 


CAUDAL   V, 


R     POSTCARDINAL  V 


AFFERENT    RENAL- 
PORTAL    VEiN 


Fig.  269. — Iguana  tuberculata,  (J.     Genito-urinary  tract,  dorsal  view,  with  renal-portal,  post- 
cardinal,  and  postcaval  veins.     (Columbia  University  Museum,  No.  1862.) 


PLATE    CXXXV. 


R.    BRACHIAL  V 

R.    PECTORAL  V 
R.    PRECAVA- 

R.      AURICLE- 
HEPATIC    VV 


P08TCAVA 
R.  COMMON  ILIAC  V 
R.    KIDNEY' 

R.    FEMORAL  V. 


R.    RENAL  V. 

divided' 
sciatic  v. 

AFFERENT    RENAL   V. 

PELVIC    V.   ENTER- 
ING   RENAL-POR- 
TAL  SYSTEM 
R.    INT.    ILiAC   V. 

RENAL-PORTAL  V. 

CAUDAL  V. 

POST.  MESENTERIC  V. 


L.  JUGULAR 
PRECARDINAL)  V. 


L.  JUGULAR   V 


L.    BRACHIAL  V. 


L.   AURICLE 

L.   VENTRICLE 

EPIGASTRIC   V. 

EFFERENT  RENAL  V. 
FEMORAL  V 

L.    RENAL  V. 
EFFERENT  RENAL  V. 

RENAL-PORTAL   V. 

COCCYGEO-MES- 
ENTERIC  VEIN 


Fig.  270. — Veins  of  pigeon,  Columba  Uvia.     (Modified  from  Parker  and  Haswell.)     The  renal- 
portal  vein  of  the  right  side  is  supposed  to  be  dissected  to  show  its  passage  through  the  right  kidney. 


PLATE    CXXXVI. 


R.  COMMON 
CAROTID  A. 


R.  SUBCLAVIAN  A. 
PRECAVA 

AZYGOS 
R.  PULMONARY  A. 

R.  PULMONARY  V. 

SINUS   VENOSUS 
OF    R.    AURICLE 

R.  HEPATIC    V. 


R      PORTAL   V 


R.   HEPATIC   V 


R.    RENAL   V 


L.  COMMON 
CAROTID    A. 


L.    BRACHIO- 
CEPHALIC   V. 


PULMONARY    A. 
AORTA 


DUCTUS    VENOSUS 
JOINING  L.   HEPATIC 
VEIN 


L.    PORTAL   V. 
ABDOMINAL  AORTA 


L.    RENAL  V. 


UMBILICAL  V. 


UMBILICAL  (HYPO- 
GASTRIC) ARTERIES 
MEETING  UMBILI- 
CAL V.    AT   CORD 


Fig.  271. — Human  foetus  at  term.      Corrosion    preparation   of  lieart  and  vascular  system. 
(Columbia  University  Museum,  No.  1858.) 


SUMMARY  OF  HEPATIC  CIRCULATION.  153 

After  birth  all  the  venous  blood  entering  the  liver  passes 
through  the  portal  vein.  In  the  right  division  the  direction  of 
the  current  is  the  same  as  in  the  foetus.  ~  ^ 

On  the  left  side,  however,  the  current  is  now  from  right 
to  left,  from  the  bifurcation  of  the  portal  into  the  channels  of 
the  left  lobe  formerly  connected  with  the  umbilical  vein  (Fig. 
261). 

Hence  the  direction  of  the  current  in  this  segment  is  reversed 
at  birth. 

SUMMARY   OF   HEPATIC   CIRCULATION. 

The  foregoing  consideration  of  the  development  shows  us  that 
the  hepatic  circulation  presents  successively  three  main  stages : 

1.  Omphalo-mesenteric  or  Vitelline  Stage,  which  results  in  the 
laying  down  of  the  primary  capillary  circulation  of  the  liver  and 
in  the  establishment  of  its  connection  with  the  developing  veins 
of  the  alimentary  tract  (primitive  portal  channels). 

2.  Umbilical  or  Placental  Stage,  in  which  the  greater  part  of  the 
blood  circulating  through  the  liver  is  oxygenated  blood  re- 
turned from  the  placenta  by  the  umbilical  vein,  accounting  for 
the  rapid  growth  and  relatively  large  size  of  the  organ  during 
foetal  life. 

The  placental  blood  uses  the  preformed  capillary  channels  of 
the  vitelline  or  primitive  portal  system  in  the  liver,  and  t  he  same 
rapidly  extend  and  enlarge  with  the  accelerated  growth  of  the 
gland.  During  this  stage  venous  blood  is  also  returned  from  the 
alimentary  tract  to  the  liver  by  the  portal  vein,  produced  by 
fusion  of  the  distal  segments  of  the  primitive  vitelline  veins  and 
their  secondary  connection  with  the  mesenteric,  splenic  and  pan- 
creatic veins  (omphalo-mesenteric  development  of  primitive  vitel- 
line veins). 

3.  Adult  or  Portal  Stage. — With  the  interruption  of  the  placental 
circulation  the  portal  vein  assumes  again  its  original  position  as 
the  only  vein  carrying  blood  to  the  liver.  With  the  establish- 
ment of  intestinal  digestion  and  absorption  this  vessel  grows 
rapidly  in  size. 


154  ANATOMY  OF  THE  PERITONEUM. 


COMPARATIVE  ANATOMY  OF  THE  HEPATIC  VENOUS 
CIRCULATION. 

For  the  purpose  of  fixing  the  main  facts  in  connection  with  the 
development  of  the  higher  mammahan  hepatic  circulation,  and 
in  order  to  obtain  a  demonstration  of  the  cycle  through  which  the 
different  veins  pass,  the  student  is  recommended  to  examine,  pref- 
erably by  personal  dissection,  a  limited  series  of  lower  vertebrates 
which  can  be  readily  procured  and  easily  injected.  The  follow- 
ing series  has  been  selected,  but  it  will  be  understood  that  other 
forms  can  be  substituted,  according  to  the  local  conditions  which 
govern  the  supply  of  the  material. 

1.  Fish.     A  Selachian,  the  common  skate  {Raja  ocellata)  or  dog- 
fish {Acanthias  vulgaris). 

2.  Amphibian. 

(a)  Urodele.     Nedurus  maculatus. 
(6)  Anura.     The  common /ro^. 

3.  Reptile. 

Preferably,  on  account  of  the  ease  of  injection,  one  of  the  larger 
lizards,  as  Iguana  tuberculata. 

The  turtles,  although  somewhat  more  difficult  objects  to  pre- 
pare, can  be  substituted. 

4.  Bird.     The  common  fowl. 

5.  Human  foetus  at  term. 

1.  Fish. — The  venous  system  can  be  injected  by  tying  a  canula 
in  the  lateral  vein,  and  injecting  both  cephalad  and  caudad,  or  by 
injecting  cephalad  through  the  caudal  vein.  The  injection  of  the 
systemic  veins  can  also  be  made  caudad  through  one  of  the  ducts 
of  Cuvier,  combined  with  an  injection  cephalad  of  the  caudal 
vein. 

The  following  main  facts  are  to  be  noted  in  the  venous  system 
of  the  Selachian  (Fig.  262) : 

1.  There  are  Two  Portal  Systems,  (a)  Renal  Portal  System. — The  cau- 
dal vein  divides  near  the  vent  into  two  branches  which  course 
along  the  lateral  border  of  the  kidneys,  sending  afferent  or  adve- 


COMPARATIVE  ANATOMY  OF  VENOUS  CIRCULATION.  155 

hent  veins  into  the  organ.  The  blood  traverses  the  renal  capil- 
laries and  is  gathered  together  by  the  efferent  or  revehent  veins, 
which  empty  into  median  paired  vessels,  the  posterior  cardinals. 
(6)  Hepatic  Portal  System. — The  veins  of  the  digestive  tract  and 
appendages  unite  to  form  a  hepatic  portal  vein.  The  blood  after 
traversing  the  capillary  system  of  the  liver  is  collected  by  hepatic 
veins,  which  form  a  dilated  hepatic  sinus  emptying  into  the  sinus 
venosus  of  the  heart. 

2.  The  middle  segment  of  the  intestine,  presenting  a  spiral 
valve  in  the  interior,  gives  rise  to  a  vein  emptying  into  the  portal 
vein  which  corresponds  to  the  subintestinal  vitelline  vein  of  the 
mammalian  embryo  (Fig.  202). 

3.  The  posterior  cardinal  veins,  also  greatly  dilated  and  forming 
the  posterior  cardinal  sinus,  join,  near  the  heart,  the  veins  return- 
ing blood  from  the  head,  the  anterior  cardinal  or  jugular,  to  form 
a  transversely  directed  trunk,  the  duct  of  Cuvier,  which  empties 
into  the  sinus  venosus  at  the  auricular  extremity  of  the  heart. 
Into  the  duct  of  Cuvier  empties  on  each  side  a  lateral  vein  return- 
ing the  blood  from  the  body  walls.  This  vein  can  be  considered, 
for  our  present  purpose,  as  representing  in  general  the  abdominal 
vein  of  amphibians  and  reptiles,  and  the  umbilical  vein  of  the 
mammalian  embryo. 

The  adult  selachian  venous  system  is  therefore  to  be  consid- 
ered as  illustrating  the  following  conditions  above  encountered  in 
our  study  of  the  embryology  of  the  mammalian  venous  system. 

1.  The  heart  illustrates  excellently  the  stage  in  the  mammalian 
development,  in  which  auricular  and  ventricular  segments  have 
dilBferentiated,  but  before  the  division  of  the  cavities  into  a  pul- 
monary and  systemic  portion  by  the  development  of  the  auric- 
ular and  ventricular  septa  and  the  division  of  the  arterial  trunk 
into  pulmonary  artery  and  aorta. 

The  sinus  venosus  still  exists,  as  an  ante-chamber  to  the  auric- 
ular cavity  proper,  receiving  on  each  side  the  ducts  of  Cuvier, 
which  represent  the  fusion  product  of  the  systemic  veins,  ante- 
rior and  posterior  cardinal. 


156  ANATOMY  OF  THE  PERITONEUM. 

2.  The  hepatic  portal  circulation  corresponds  to  the  mamma- 
lian stage  in  which  the  vitelline  veins  have  become  omphalo- 
mesenteric  by  joining  the  intestinal  veins. 

The  spiral  vein  remains  as  a  portion  of  the  original  vitelline 
vein  corresponding  to  the  subintestinal  segment  of  the  mamma- 
lian embryo  (cf  Figs.  248  and  249). 

The  selachian  portal  vein  represents  the  united  vitelline  veins, 
into  which  the  veins  of  the  digestive  tract  open. 

In  the  liver  we  find  a  simple  system  of  vense  advehentes,  de- 
rived from  the  branching  of  the  portal  vein,  a  hepatic  capillary 
network,  and  vense  revehentes,  the  proximal  remnants  of  the 
original  vitelline  veins  which  carry  the  liver  blood  to  the  sinus 
venosus.  The  condition  of  the  hepatic  circulation  corresponds 
therefore  to  the  stage  shown  in  Fig.  250  of  the  mammalian  de- 
velopment. There  is  as  yet  no  association  of  the  hepatic  venous 
system  with  the  representative  of  the  umbilical  vein  ( the  lateral 
vein  of  the  selachian). 

3.  The  lateral  veins,  which  we  can,  as  stated,  regard  for  pur- 
poses of  illustration,  without  prejudging  their  genetic  significance, 
as  representing  the  mammalian  embryonic  umbilical  veins,  still 
present  the  condition  corresponding  to  the  early  mammalian 
embryonal  stage  shown  in  Fig.  250.  They  are  veins  of  the  body 
walls,  emptying  cephalad  of  the  liver,  directly  into  the  ducts  of 
Cuvier,  and  through  them  into  the  sinus  venosus  of  the  heart. 

Fig.  262  shows  the  arrangement  of  the  venous  system  in  a 
typical  selachian  diagrammatically. 

2.  Amphibian,  (a)  Urodele. — The  following  points  are  to  be  noted 
in  comparison  with  the  preceding  form : 

1.  The  two  ducts  of  Cuvier  entering  into  the  sinus  venosus  are 
formed  by  the  anterior  cardinal  and  subclavian  veins,  which 
latter,  having  appeared  with  the  full  development  of  an  anterior 
extremity,  receives  the  posterior  cardinal  veins,  representing  the 
mammalian  azygos  system. 

2.  The  renal  portal  circulation  persists.  The  caudal  vein  is, 
however,  no  longer  the  only  afferent  vein  of  this  system.     With 


COMPARATIVE  ANATOMY  OF  VENOUS  CIRCULATION.  157 

the  full  development  of  a  posterior  extremity  an  iliac  vein  re- 
turns the  blood  from  the  same  and  gives  a  large  branch  (afferent 
to  the  portal  renal  system),  while  the  trunk  continues  cephalad 
as  an  anterior  abdominal  vein,  corresponding  to  the  lateral  sela- 
chian vein,  emptying  in  the  hepatic  portal  vein. 

3.  The  efferent  veins  of  the  renal  portal  system  no  longer  unite 
to  form  the  posterior  cardinal,  as  in  the  Selachian,  but  empty  into 
a  new  median  vessel,  the  inferior  vena  cava,  or  postcava,  which 
has  replaced  the  distal  segments  of  the  posterior  cardinal  veins. 

The  postcava  now  carries  the  blood  from  the  kidneys  directly  to 
the  heart.  The  original  posterior  cardinal  veins  still  persist  in 
their  proximal  segments,  as  smaller  trunks  connecting  the  distal 
part  of  the  postcava  with  the  ducts  of  Cuvier  through  the  sub- 
clavian veins.  The  ducts  of  Cuvier  represent  the  precavse  (vense 
cavse  superiores)  of  mammalia  and  the  postcardinals  the  mam- 
malian azygos  veins. 

4.  The  hepatic  portal  system  differs  in  two  respects  from  the 
Selachian  type. 

(a)  The  blood  returned  to  the  liver  from  the  digestive  tract  by 
the  portal  vein  becomes  mixed  before  entering  the  gland  with  the 
blood  returned  from  the  posterior  extremities  and  abdominal 
walls  by  the  abdominal  vein. 

This  vein,  paired  below  and  continuous  with  the  lateral  of  the 
two  branches  into  which  the  iliac  vein  divides,  becomes  united 
into  a  single  trunk  above  and  empties  into  the  portal  vein. 

The  abdominal  vein  represents  the  lateral  vein  of  the  Selachian 
and  corresponds  to  the  umbilical  vein  of  the  higher  vertebrates. 

(h)  The  vense  hepaticse  revehentes  do  not  empty  directly  into 
the  sinus  venosus,  but  into  the  proximal  portion  of  the  postcava. 

Hence  the  adult  urodele  venous  system  illustrates,  in  reference 
to  the  mammalian  development,  these  stages : 

1.  The  umbilical  (abdominal)  vein  has  lost  its  direct  connection 
with  the  sinus  venosus.  The  proximal  segment,  cephalad  of  the 
liver,  has  disappeared,  and  its  blood  now  passes  directly  into  the 
hepatic  circulation  by  its  union  with  the  portal  vein. 


158  ANATOMY  OF  THE  PERITONEUM. 

(Cf.  stage  schema  Figs.  251  and  252.) 

2.  The  postcaval  vein  has  made  its  appearance,  largely  replac- 
ing the  posterior  cardinal  veins,  whose  proximal  segments  became 
converted  into  secondary  vessels  (azygos)  uniting  the  system  of 
the  postcava  with  that  of  the  duct  of  Cuvier  (mammalian  prae- 
cava),  while  their  distal  segments  are  transformed  into  the  distal 
portion  of  the  postcava. 

The  postcava,  therefore,  is  made  up  of  two  districts  : 

{a)  The  proximal  portion  is  a  new  vessel,  developed  in  connec- 
tion with  the  hepatic  venous  system. 

(6)  The  distal  portion  is  derived  from  the  distal  segments  of  the 
original  posterior  cardinal  veins. 

The  termination  of  the  hepatic  veins  in  the  postcava  corre- 
sponds to  the  stage  shown  in  schema  Fig.  256. 

Fig.  263  gives  a  schematic  representation  of  the  arrangement  of 
the  venous  system  in  a  typical  urodele  amphibian  {Salamandra 
maculosa). 

In  Fig.  264  the  dissected  venous  system  of  Necturus  rrMculatvs, 
the  mud  puppy,  is  shown  in  an  injected  preparation. 

(6)  Anure. — The  venous  system  of  Rana  esculenta  is  shown  in 
Fig.  265.     Comparison  with  venous  system  of  urodele  : 

1.  The  abdominal  vein,  corresponding  to  the  mammalian  um- 
bilical vein,  has  assumed  a  greater  importance  in  reference  to  the 
hepatic  circulation.  It  is  a  large  trunk,  continuous  below  with 
the  pelvic  vein,  terminating  above  in  two  branches,  which  enter 
the  liver  as  afferent  veins,  being  joined  just  prior  to  the  division 
by  the  hepatic  portal  vein. 

2.  A  small  cardiac  vein,  coming  from  the  heart,  empties  into 
the  angle  of  bifurcation  of  the  abdominal  vein. 

3.  The  postcava  is  well  developed,  formed  by  large  efferent 
renal  veins.  It  entirely  replaces  the  posterior  cardinal  veins 
which  are  absent  in  the  adult  animal. 

4.  A  right  and  left  prsecaval  vein  is  formed  by  the  union  of 
two  jugular  trunks  with  the  vein  of  the  anterior  extremity  an  da 
large  musculo-cutaneous  vein. 


COMPARATIVE  ANATOAfY  OF  VENOUS  CIRCULATION.  159 

Comparison  with  the  mammaHan  development :  the  venous 
system  of  this  amphibian  can  be  used  to  illustrate  the  mamma- 
lian embryonal  stage  shown  in  schema  Fig.  252,  in  which  the  ab- 
dominal or  umbilical  vein  has  become  the  most  important  vessel 
in  the  afferent  hepatic  venous  system. 

The  communication  existing  by  means  of  the  cardiac  vein  be- 
tween the  heart  and  the  hepatic  afferent  system  may  suggest,  but 
purely  for  illustrative  purposes,  the  direct  connection  of  the  um- 
bilical vein  with  the  heart  by  the  ductus  venosus  in  the  mam- 
malian embryo  (cf.  schema  Figs.  250-256). 

3.  Reptile. — In  Iguana  the  renal  portal  system  is  well  developed. 
The  caudal  vein,  returning  the  blood  from  the  tail  and  the  cavern- 
ous tissue  of  the  genital  organs,  continues  for  a  short  distance  upon 

the  fused  caudal  end  of  the  two  kidneys  (Fig,  269)  and  then 

> 

divides  into  two  afferent  renal  veins  which  ascend  on  the 
ventral  surface  of  the  glands,  giving  branches  to  the  renal  cap- 
illary system.  About  the  middle  of  the  kidney  each  afferent 
vein  is  joined  by  a  large  transverse  branch  from  the  abdominal 
vein  (Fig.  266). 

The  renal  efferent  system  begins  by  a  number  of  interrenal 
anastomoses  which  unite  along  the  mesal  border  of  the  right  kid- 
ney into  a  large  ascending  trunk,  while  the  corresponding  vessel 
of  the  left  side,  starting  from  the  same  anastomosis,  is  consider- 
ably smaller  (Figs.  266  and  269).  Each  of  these  vessels  also  re- 
ceives blood  from  the  testis,  epididymis,  vas  deferens  and  adrenal 
body  in  the  male,  and  from  the  ovary  and  oviduct  in  the  female. 
They  represent,  in  fact,  the  distal  functional  part  of  the  right  and 
left  embryonic  postcardinal  vein.  Just  caudad  of  the  left  testis  the 
vein  of  the  left  side  crosses  obliquely  ventrad  of  the  aorta  and  joins 
the  right  vessel  to  form  the  trunk  of  the  postcava,  which  enters, 
immediately  beyond  the  cephalic  pole  of  the  right  testis,  the 
prolonged  caval  lobe  of  the  liver  (Figs.  266  and  269).  Ascending 
in  the  substance  of  this  gland  and  receiving  the  afferent  hepatic 
veins  (Fig.  268),  the  vena  cava  emerges  from  the  cephalic  surface 
of  the  liver  greatly  enlarged  and  proceeds  to  the  right  auricle. 


160  ANATOMY  OF  THE  PERITONEUM. 

The  abdominal  vein  divides  below  into  two  branches  which 
pass  caudad  on  each  side  of  the  bladder,  receiving  tributaries 
from  the  same,  to  the  lateral  border  of  the  kidneys  (Figs.  266 
and  269).  Here  the  vessel  is  connected  by  the  transverse  branch 
above  described  with  the  afferent  renal  portal  system  derived 
from  the  caudal  vein.  At  the  same  point  it  receives  the  sciatic 
vein,  the  principal  venous  vessel  of  the  posterior  extremity. 
Above,  the  main  abdominal  vein,  resulting  from  the  union  of  the 
two  branches  referred  to,  ascends  on  the  dorsal  surface  of  the 
ventral  abdominal  wall,  receiving  a  few  twigs  from  the  ventral 
mesogastrium  within  whose  free  caudal  edge  the  vessel  runs. 
Just  before  reaching  the  liver  the  abdominal  vein  turns  dorsad 
on  the  caudal  surface  of  the  gland  and  joins  the  hepatic  portal 
vein  (Figs.  268  and  275).  Several  accessory  veins,  two  or  three 
in  number,  belonging  to  the  system  of  the  abdominal  vein,  pass 
above  this  point  from  the  ventral  body  wall  between  the  layers 
of  the  ventral  mesogastrium,  to  enter  the  liver  separately  on  its 
convex  ventral  surface,  above  the  fusion  of  the  main  abdominal 
vein  with  the  portal  vein.  These  additional  branches  on  entering 
the  liver  join  the  portal  system,  forming  a  set  of  ventral  accessory 
portal  veins. 

The  hepatic  portal  vein  derives  its  principal  tributaries  from 
the  splenic,  gastric,  pancreatic  and  intestinal  veins.  One  or  two 
additional  branches  (accessory  vertebral  portal  veins),  as  above 
stated,  connect  the  system  of  the  segmental  and  vertebral  veins 
with  the  portal  circulation,  entering  the  liver  separately.  In  like 
manner  one  or  two  gastric  veins  (accessory  gastric  portal  veins) 
enter  the  dorsal  aspect  of  the  liver  separately,  passing  from 
the  stomach  to  the  gland  between  the  layers  of  the  gastro-hepatic 
omentum  (Fig.  275). 

Compared  with  the  development  of  the  mammalian  type,  the 
venous  system  of  Iguana  serves  to  illustrate  the  stage  in  the  his- 
tory of  the  umbilical  vein  (represented  by  the  abdominal  vein  of 
the  reptile)  in  which  the  connection  of  the  vessel  with  the  portal 
vein  has  been  formed  and  transmits  the  greater  part  of  the  blood 


PLATE   CXXXVII. 


R.    INT.    JUGULAR    V 

INF.    THYROID   V 

R.    EXT.    JUGULAR    V 

INF.    THYROID    V. 

R.    SUBCLAVIAN    V. 

R.   INT.   IMAMMARY  V. 

PRECAVA 


SUP.    INTER- 
COSTAL V. 


COMMON  AZYGOS  V 


V.    AZYGOS    MAJOR 


POSTCAVA   DIVIDED 

AT    ENTRANCE-f^ 
INTO    LIVER 


R.    RENAL   V 


QUADRATUS 
LUMBORUM 


R.    SPERMATIC   V 


L.    INT.   JUGULAR   V. 
INF.    THYROID    V. 
L.    EXT.   JUGULAR    V. 

L.    SUBCLAVIAN    V. 
L.    BRACHIO- 
CEPHALIC   V. 
L.    INT.    MAMMARY    V. 
L.    SUP.    INTER- 
COSTAL  V. 


L.    INTERMEDIATE 
AZYGOS    FROM    5TH, 
6TH     AND  7TH 
SPACES 


V.   AZYGOS    MINOR 


—  L.    RENAL  V 


-r t<k}tS L.   SPERM/ 


L.   COMMON    ILIAC   V. 


Fig.  272.— Human   foetus  at  term.      Postcava  and   azygos  veins.      (Columbia    University 
Museum,  No.  18G1.) 


PLATE    CXXXVIII. 


DIAPHRAGM  WITH 
ATTACHED    SUR- 
FACE   OF    LIVER 


VENTRAL     MESO- 
GASTRIUM        FORM- 
ING      SUSPENSORY 
LIGAMENT  OF  LIVER 
VENTRAL      MESO- 
GASTRIUM   FORMING 
GASTRO-HEPATIC 
OMENTUM 

BILE-DUCT 


FREE    EDGE    OF 
SUSPENSORY    LIGA- 
MENT   OF    LIVER 


CESOPHAGUS 


DORSAL    MESO- 
GASTRIUM 


STOMACH 


DUODENUM 


\ 


Fig.  273. — Schematic  profile  view  of  veutral  mesogastrium  with  developing  liver. 


PARIETAL 
PERITONEUM 


VENTRAL    MESO 
GASTRIUM   FORM- 
ING SUSPENSORY 
LIGAMENT 

LIVER 


VENTRAL    MESO- 
GASTRIUM   FORMING 
CASTRO-HEPATIC 
OMENTUM 


DORSAL    MESO- 
GASTRIUM 


Fig.  274. — Schematic  trausectiou  of  abdomeu  in  region  of  ventral  mesogastrium. 


PLATE    CXXXIX. 


CESOPHAGUS 


DORSAL    MESO- 
GASTRIUM 


SMALL 
INTESTINE 


DORSAL 
MESENTERY 


CEPHALIC  END  OF  POST- 
CAVA      EMERGING     FROM 
LIVER    TO     ENTER     PERI- 
CARDIUM 
VENTRAL  ABD.  WALL 

VENTRAL  MESOGASTR. 
ISUSPENS.  LIG.)  WITH 
ACCESSORY  VENTRAL 
PORTAL   VEINS 

VENTRAL  MESOGASTR. 
IGASTRO-HEPATIC  LIG.) 


ABDOMINAL   V 
PORTAL   V. 


CAUDAL    END   OF    POST- 
CAVA  ENTERING  LIVER 


Fia.  275. — Abdominal  viscera  of  Iguana  tuberculata,      (Columbia   University 
Museum,  No.  1313.) 


LAYERS  OF    LEFT 
CORONARY    LIG. 


IS  OF  GASTRO- 
HEPATIC    LIG. 


ILICAL  VEIN    IN 
:   EDGE  OF  FAL- 
CIFORM   LIG. 


LAYERS  OF  FALCI- 
FORM OR  SUSPEN- 
SORY   LIGAMENT 


LAYERS  OF  RIGHT 
CORONARY    LIG. 

NON-PERITONEAL 
PHRENIC  SURFACE 
OF    LIVER 


Fig.  276. — Schematic  view  of  embryonic  liver  detached   from  its  connections,   seen   from, 
behind,  with  lines  of  peritoneal  reflection. 


PLATE    CXL. 


DUCTUS  VENOSUS 


VENA  CAVA  RECEIV- 
ING RIGHT  AND  LEFT 
HEPATIC    VEINS 


PORTAL    VEIN 


UMBILICAL  VEIN 


Fig.  277. — Schematic  view  of  embryonic  liver,  showing  influence  of  vascular  connections  on 
the  arrangement  of  the  lines  of  peritoneal  reflection. 


LEFT  CORONARY  LIG. 


DUCTUS  VENOSUS 

LESSER  OMENTUM 

ALONG   FISSURE   FOR 

DUCTUS  VENOSUS 


UMBILICAL  VEIN 


SUSPENSORY    LIG 


LEFT    HEPATIC   VEIN 
RIGHT   HEPATIC    V. 
R.   CORONARY    LIG. 

NON-PERITONEAL 
PHRENIC  SURFACE 

POSTCAVA 
SPIGELIAN    LOBE 
CAUDATE    LOBE 


PORTAL   VEIN 

LESSER  OMENTUM 
AT    TRANSVERSE 
FISSURE 


FiG;  278.— Later  stages,  showing  development  of  transverse  fissure,  Spigelian  and  caudate  lobes. 


SPIGELIAN    LOBE 
FISSURE    FOR  DUC- 
TUS VENOSUS  WITH 
VERTICAL   SEGMENT 
OF  LESSER  OMENTUM 

LEFT    LOBE 


UMBILICAL  FISSURE 


UMBILICAL  VEIN  IN 
FREE  EDGE  OF  FAL- 
CIFORM   LIGAMENT 


LAYERS  OF  RIGHT 
CORONARY    LIG. 
NON-PERITONEAL 
PHRENIC  SURFACE 
OF  RIGHT   LOBE 
POSTCAVA 

CAUDATE    LOBE 
PORTAL  VEIN    BETW.    LAYERS 
OF    LESSER   OMENTUM    AT 
TRANSVERSE     FISSURE 
RIGHT    LOBE 


QUADRATE    LOBE 


Fig.  279. — Liver  of  human  foetus  at  eighth  mouth. 
(Columbia  University  Museum,  No.  1854.) 


View  of  caudal  and  dorsal  surfaces. 


PLATE    CXLI. 


SUSPENSORY    LIG. 


SPIGELIAN   LOBE 


L.  TRIANGULAR  LIG. 

FISSURE    FOR    DUC- 
TUS VENOSUS 

LEFT    LOBE 


FISSURE   FOR  UM- 
BILICAL  VEIN 


POSTCAVA  RECEIVING 
HEPATIC  VEINS 

NON-PERITONEAL 
SURFACE  OF  RIGHT 
LOBE   BETW.    LAYERS 
OF  R.   CORONARY   LIG. 
R.  TRIANGULAR   LIG. 
POSTCAVA 

CAUDATE    LOBE 
TRANSV.    FISSURE 

RIGHT    LOBE 


GALL-BLADDER 


QUADRATE    LOBE 


Fig.  280.— Human  fojtal  liver  at   term,  showing  lines  of  peritoneal  reflection   on 
cephalic,  dorsal,  and  caudal  surfaces.     (Columbia  University  Museum,  No.  1855.) 


SUSPENSORY 
LIGAMENT 


CORONARY  LIG. 
FISSURE     FOR    DUC- 
TUS VENOSUS    WITH 
VERTICAL    SEGMENT 
OF  LESSER  OMENTUM 
SPIGELIAN    LOBE 

LESSER  OMENTUM 

ALONG  TRANSVERSE 

FISSURE 


LEFT    LOBE 
FISSURE   FOR  UM- 
BILICAL  VEIN 
(round  LIG.) 


CEPHALIC   END    OF 
HEPATIC  SEGMENT 
OF    POSTCAVA 
DIAPHRAGM 


CAUDAL  END  OF 
HEPATIC  SEGMENT 
OF    POSTCAVA 

CAUDATE    LOBE 


GALL-BLADDER 


QUADRATE    LOBE 


RIGHT    LOBE 


Fig.  281. — Liver  of  cat,  hardened  in  situ.     (Columbia  University  Museum,  No.  1836.) 


ATTACHMENT       OF 
GASTRO-HEPATIC 
OMENTUM  TO    LES- 
SER   CURVATURE 


VERTICAL  SEGMENT 
OF  GASTRO-MEPATIC 
OMENTUM  ATTACHED 
TO  FISSURE  OF  DUC- 
TUS   VENOSUS 

TRANSV.  SEGMENT 
OF  GASTRO-HEPATIC 
OMENTUM  ATTACHED 
TO  TRANSV.    FISSURE 


Fig.  282. — Dorsal  view  of  human  liver  and  stomach  in  foetus  at  term,  show- 
ing lines  of  hepatic  and  gastric  attachment  of  lesser  omentum. 


PLATE    CXLII. 


FALCIFORM    LIG 


L.    CORONARY    LIG. 


CORONARY    LIG. 


POSTCAVA 


Fig.  283. — Schema  of  lines  of  reflection  of  peritoneum  on  dorsal  surface  of  liver  and  in  the 
formation  of  the  gastro-hepatic  omentum.  A  B,  transverse  section  of  lesser  omentum  attached  to 
transverse  fissure  of  liver  and  to  pyloric  section  of  lesser  curvature  (.4'  B');  B  C,  vertical  section 
of  lesser  omentum  passing  between  fissure  of  ductus  venosus  and  cardiac  section  of  lesser  cur- 
vature of  stomach  {B'  C) ;  CD,  line  of  reflection  of  peritoneum  from  cephalic  border  of  Spigelian 
lobe  to  diaphragm  ;  D  E,  line  of  reflection  of  peritoneum  from  right  border  of  Spigelian  lobe  to 
left  margin  of  postcava  and  diaphragm. 


C  ANGLE  OF  LESSER  OMENTUM 
AT  JUNCTION  OF  TRANSV.  FISSURE 
AND  FISSURE  FOR  DUCTUS  VENOSUS 


-S.  LESSER  OMENTUM  AT- 
TACHED TO  FISSURE  FOR 
DUCTUS    VENOSUS 


-<1-    LESSER  OMENTUM 

ATTACHED   TO  TRANSV. 

FISSURE 


GALL-BLADDER 

SPIGELIAN   LOBE 

CRUS  OF  DIAPHRAGM 

R.   EDGE  OF    LESSER 

OMENTUM   (lIG.   HE- 

PATO-DUODENALE) 

R.  PANCREATICO- 
GASTRIC  FOLD  CAR- 
RYING   HEPATIC    ART, 


PYLORIC     END 
OF    STOMACH 
SUPRACOLIC    SEGMENT 
OF    DESC.     DUODENUM 
ATTACHMENT       OF      HE- 
PATIC     FLEXURE    OF 
COLON   'tRANSV.    MESO- 
COLON)     TO       VENTRAL 
SURFACE     OF    DESCEND- 
ING    DUODENUM 

INFRACOLIC     SEGMENT 
OF   DESC.    DUODENUM 


DEXTRO-MESENTERIC       SUPERIOR 


SINISTRO-MES  ENTERIC 


SEGMENT     OF    TRANS- 
VERSE   DUODENUM 


MESENTERIC     SEGMENT       OF      TRANS- 
VESSELS  VERSE    DUODENUM 
ENTERING 
ROOT    OF 
MESENTERY 


GASTRIC    IMPRESSION 
OF    LEFT    LOBE 


CARDIA    OF    STOMACH 


SPLEEN,    GAS- 
TRIC SURFACE 

L.  PANCREATICO-GAS- 
TRIC  FOLD  CARRYING 
CORONARY   ART. 

L.    ADRENAL 

SPLENIC   ART. 
AND    VEIN 

PANCREAS     VEN- 
TRAL  SURFACE 

CEPHALIC  LAYER, 

TRANSVERSE 

MESOCOLON 

CAUDAL  LAYER, 

TRANSVERSE 

MESOCOLON 


ASCEND.    DUODENUM 


Fig.  284. — Portion  of  abdominal  viscera  of  adult  human  subject,  hardened  in  situ.  (Colum- 
bia University,  Study  Collection.)  The  segment  of  stomach  between  cardiac  and  pyloric  orifices 
has  been  removed,  dividing  the  lesser  omentum  to  this  extent,  but  leaving  the  right  extremity  of 
the  membrane  (lig.  hepato-duodeuale)  intact.  Behind  this  portion  the  arrow  passes  through  the 
foramen  of  Wioslow. 


PLATE   CXLIII. 


ANT.    (quadrate)    LOBE 


GASTRO-HEPATIC 

OMENTUM  ALONG 

TRANSV.    FISSURE 

R.    LOBE 


GASTRO-HEPATIC 
OMENTUM  ALONG 
FISSURE  OF  DUC- 
TUS   VENOSUS 

GASTRO-HEPATIC 
OMENTUM  ALONG 
LESSER  CURVATURE 

STOMACH 


Fig.  285. — Liver  and  stomach  of  Macacus  pileatus.     (Columbia  Univer- 
sity, Study  Collection.) 


UMBILICAL 
FISSURE 

LESSER   OMENTUM 

ALONG   FISSURE    FOR 

DUCTUS  VENOSUS 


LESSER    OMENTUM 

ALONG  transverse: 

FISSURE 


l.  triangular  lig. 
(hg.    hepatico- 
phrenicum) 
gastro-phrenic 
ligament 

-spigelian  lobe 


Fig.  286.— Abdominal  viscera  of  adult  human  subject,  hardened  in  situ:  with  liver  lifted  up 
after  mcision  of  the  gastro-hepatic  omentum.     (Columbia  University  Museum,  No.  1845.) 


PLATE   CXLIV. 


VENTRAL    MESO- 
GASTRIUM 


HEPATIC  ART. 


DUODENUM 


DORSAL    MESO- 
GASTRIUM 


MESODUODENUM 


Fig.  287. — Primitive  dorsal  and  ventral  mesogastrium  with  course  of  hepatic 
artery. 


VENTRAL  MESO- 
GASTRIUM 


HEPATIC    DUCT 


DUODENUM 


DORSAL  MESO- 
GASTRIUM 


STOMACH 


HEPATIC    ART 
PANCREAS 

MESODUODENUM 


Fig.  288.— The  liver  divides  the  ventral  mesogastrium  into  a  dorsal  seg- 
ment, the  gastro-hepatic  or  lesser  omentum,  and  a  ventral  segment,  the  suspensory 
or  falciform  ligament  of  the  liver. 


COMPARATIVE  ANATOMY  OF  VENOUS  CIRCULATION.  161 

returned  by  the  umbilical  vein  to  the  liver,  while  the  proximal 
segment  above  this  point,  originally  continued  into  the  sinus 
venosus,  has  begun  to  disappear,  being,  however,  still  represented 
by  the  vessels  which,  as  accessory  ventral  portal  veins,  pass  in  the 
ventral  mesogastrium,  from  the  body  wall  to  the  liver. 

It  will  be  noted  that  all  the  hepatic  portal  blood,  whether  con- 
ducted by  the  main  portal  and  abdominal  vein,  or  by  the  acces- 
sory portal  branches,  traverses  the  capillary  circulation  of  the 
liver  before  entering  the  postcava. 

The  vertebral  and  segmental  venous  system,  representing  the 
azygos  veins  of  the  mammalia,  is  very  rudimentary  (Figs.  266 
and  267).  The  distal  portions  of  the  postcardinal  veins  form  the 
efferent  renal  branches  and  the  ascending  trunks  of  the  postcava. 

The  next  segment  of  the  vertebral  veins  appears  as  a  trunk  on 
the  right  side  which  enters  the  portal  circulation.  A  second  vein 
higher  up  is  connected  with  both  the  gastric  portal  system  and  with 
the  longitudinal  chain  of  the  vertebral  veins.  Finally  a  proximal 
venous  branch  on  each  side  of  the  vertebral  column,  representing 
the  upper  portion  of  the  postcardinal  veins,  receives  the  proximal 
segmental  veins  and  empties  into  the  subclavian  vein  (Fig.  267). 

4.  Bird. — The  characteristic  change  in  the  venous  system  of 
the  bird,  as  compared  with  that  of  the  amphibian  and  reptile,  is 
found  in  the  nearly  complete  abolition  of  the  renal  portal  system. 
The  caudal  vein  bifurcates,  sending  on  each  side  a  large  trunk, 
which  receives  the  pelvic  (int.  iliac)  veins,  to  the  kidney  (renal 
afferent  portal  vein),  but  only  a  few  small  branches  enter  the  sub- 
stance of  the  gland  (Fig.  270,  afferent  renal  V).  The  main  ves- 
sel continues  cephalad  through  the  kidney  and,  after  receiving 
the  vein  from  the  posterior  extremity  (femoral),  unites  as  common 
iliac  vein  with  the  vessel  of  the  opposite  side  to  form  the  post- 
cava. This  vessel  traverses  the  liver,  receiving  the  hepatic  affer- 
ent veins  of  the  portal  system.  The  portal  vein  is  formed  by 
tributaries  from  the  intestinal  canal,  pancreas  and  spleen,  and  is 
also  joined  by  a  large  coccygeo-mesenteric  vein,  which  is  given 

off  at  the  point  of  bifurcation  of  the  caudal  vein  and  receives 
11 


162  ANATOMY  OF  THE  PERITONEUM. 

tributaries  from  the  lower  part  of  the  alimentary  canal.  The 
abdominal  vein  of  amphibians  and  reptiles  is  represented  prob- 
ably by  the  epigastric  vein,  which  returns  the  blood  from  the 
omental  mass  of  fat  to  the  hepatic  veins. 

Compared  with  the  mammal  on  the  one  hand,  and  with  the 
lower  types  on  the  other,  the  venous  circulation  of  the  bird  illus- 
trates the  following  points : 

1.  Extensive  reduction  of  the  renal  portal  system  and  direct 
formation  of  postcava  by  the  iliac  veins,  foreshadowing  the  con- 
dition found  in  the  mammal. 

2.  Complete  separation  of  the  portal  and  systemic  venous  cir- 
culation in  the  adult.  Disappearance  of  the  ventral  abdominal 
vein  as  a  vessel  of  the  body  wall. 

5.  Human  Foetus  at  Term. — The  student  is  recommended  to  ex- 
amine, by  dissection  and  injection,  the  venous  system  of  a  foetus 
at  term,  noting  the  following  facts : 

1.  Course  of  umbilical  vein  in  ventral  abdominal  wall  and  along 
free  edge  of  falciform  ligament  to  liver  (Fig.  241),  correspond- 
ing to  the  position  of  the  amphibian  and  reptilian  abdominal 
vein  (Figs.  264  and  275). 

2.  Connection  of  umbilical  vein  in  liver : 

(a)  With  portal  system  (Figs.  258  and  271). 
(a)  With  portal  vein. 

(/8)  With  portal  system  of  left  and  quadrate  lobes  by 
branches   derived  directly  from  umbilical  vein  while 
situated  in  the  umbilical  fissure  (Fig.  258). 
(6)  With  hepatic  veins  and  postcava  by  the  ductus  venosus 
(Figs.  258  and  271). 

3.  Connection  of  the  postcaval  and  precaval  systems  by  the 
azygos  veins  representing  the  proximal  segments  of  the  embryonic 
postcardinal  veins  (Fig.  272). 

If  possible  the  dissection  of  an  injected  foetus  should  be  com- 
bined with  the  examination  of  corrosion  preparation  of  the  fcetal 
circulation  and  especially  of  the  venous  system  of  the  foetal  liver 
(Figs.  258  and  271). 


THE   VENTRAL  MESOGASTBIUM.  163 

3.  The  remnants  of  foetal  structures  in  the  adult  liver  (round 
ligament  and  ligament  of  the  ductus  venosus)  should  be  com- 
pared with  the  structures  from  which  they  are  derived  in  the 
foetus  at  term  (umbilical  vein  and  ductus  venosus). 

II.    THE  VENTRAL  MESOGASTRIUM. 

This  membrane  has  been  heretofore  mentioned  on  several  occa- 
sions. It  now  remains  for  us  to  carefully  consider  its  arrange- 
ment in  detail,  both  as  regards  the  peritoneal  relations  of  the  liver 
and  in  reference  to  its  influence  on  the  abdominal  space  as  a 
whole.  We  can  best  accomplish  this  purpose  by  considering  the 
membrane  in  the  first  place  in  a  purely  schematic  manner.  In 
contradistinction  to  the  primitive  common  dorsal  mesentery, 
which  extends  the  entire  length  of  the  alimentary  tube,  the  ven- 
tral mesentery,  or  properly  the  ventral  mesogastrium,  is  confined 
to  the  stomach  and  proximal  portion  of  the  duodenum.  We  can 
represent  the  membrane  as  extending  between  the  ventral  ab- 
dominal wall  and  the  ventral  border  (later  the  lesser  curvature) 
of  the  stomach  and  of  the  hepatic  angle  of  the  duodenum. 
Cephalad  it  is  connected  with  the  embryonic  septum  transversum 
(future  diaphragm).  Caudad  its  two  layers  pass  into  each  other 
in  a  free  concave  edge,  including  between  them  the  umbilical 
vein  (free  edge  of  falciform  ligament  of  adult) .  Consequently  a 
schematic  profile  or  lateral  view  of  the  membrane  and  its  attach- 
ments in  the  earlier  stages  would  appear  as  represented  in  Fig. 
273,  while  the  arrangement  in  transection  would  be  as  shown  in 
Fig.  274.  It  will  be  observed  that  the  separation  of  the  cephalic 
portion  of  the  abdominal  cavity  into  symmetrical  right  and  left 
halves,  previously  indicated  in  discussing  the  primitive  stomach 
and  the  dorsal  mesogastrium,  is  actually  completed  by  the  ven- 
tral mesogastrium.  This  complete  separation  of  the  lateral 
halves  of  the  coelom  cavity  ceases  at  the  point  where  the  ventral 
mesogastrium  terminates  in  the  free  concave  edge  carrying  the 
umbilical  vein.  Hence  caudad  of  this  falciform  edge  the  two 
halves  of  the  cavity  communicate  freely  with  each  other  ventrad 
of  the  intestine  and  dorsal  mesentery. 


164  ANATOMY  OF  THE  PERITONEUM. 

This  difference  in  the  extent  of  the  mesogastria  is  perhaps  best 
■understood  by  reference  to  their  relation  to  the  first  portion  of  the 
duodenum.  We  have  seen  that  the  duodenum  in  the  early  stages 
is  attached  dorsally  by  a  portion  of  the  common  dorsal  mesen- 
tery, which,  after  differentiation  of  the  intestinal  tract,  immedi- 
ately follows  the  dorsal  mesogastrium  proper,  forming  the  meso- 
duodenum  (Fig.  172).  The  proximal  portion  of  the  duodenum 
(hepatic  angle)  is  still  included  within  the  fold  of  the  ventral 
mesogastrium  which  membrane  terminates  immediately  beyond 
this  point  in  the  free  edge  surrounding  the  umbilical  vein 
(subsequent  round  ligament)  (Fig.  172).  The  remainder  of 
the  duodenum  is  devoid  of  any  ventral  attachment,  being  only 
connected  to  the  dorsal  body  wall  by  the  mesoduodenum  (Fig. 
197). 

Subsequently,  after  the  fourth  month,  while  the  right  surface 
of  the  mesoduodenum  and  descending  duodenum  adhere  to  the 
parietal  peritoneum,  the  peritoneal  investment  of  the  first  por- 
tion or  hepatic  angle  remains  free.  This  p^itoneal  covering  of 
the  proximal  duodenal  segment  is  situated  at  the  point  where  the 
caudal  end  of  the  ventral  mesogastrium,  after  surrounding  the 
first  portion  of  the  duodenum,  becomes  continuous  with  the  dor- 
sal mesentery  forming  the  mesoduodenum.  Obliteration  of  the 
latter  membrane  by  adhesion  to  the  parietal  peritoneum  leaves 
the  first  portion  of  the  duodenum  invested  on  both  surfaces  by 
the  lesser  omentum,  derived  from  the  ventral  mesogastrium.  The 
ventral  surface  of  the  gut  is  covered  by  the  ventral  layer,  the 
dorsal  surface  by  the  dorsal  layer  of  the  lesser  omentum.  These 
two  layers  become  continuous  around  the  right  free  edge  of  the 
lesser  omentum  (hepato-duodenal  ligament)  forming  the  ventral 
boundary  of  the  foramen  of  Winslow  (cf  infra,  p.  177). 

Returning  to  the  schematic  consideration  of  the  ventral  meso- 
gastrium above  outlined  (Figs.  273  and  274)  we  have  to  note  the 
first  important  change  in  the  arrangement  depending  upon  the 
development  of  the  liver.  This  organ,  growing,  as  we  have  seen, 
from  the  duodenum,  extends  between  the  two  layers  of  the  ven- 


I 


THE   VENTRAL  MESOGASTBIUM.  165 

tral  mesogastrium,  receiving  a  serous  investment  from  the 
same.  At  an  early  period  the  hver,  developing  thus  between 
the  mesogastric  layers,  reaches  the  septum  transversum  and 
becomes  closely  connected  with  it,  laying  the  foundation  for 
the  subsequent  extensive  attachment  of  the  gland  to  the  dia- 
phragm. 

Extending  caudad  the  liver  grows  beyond  the  caudal  free  edge 
of  the  ventral  mesogastrium  on  each  side,  carrying  the  serosa  with 
it.  Consequently  the  ventral  margin  of  the  liver  becomes  in- 
dented at  this  point ;  the  umbilical  vein  and  subsequently  its 
fibrous  remnant,  the  round  ligament,  are  imbedded  in  a  notch 
and  fissure  (umbilical  notch  and  fissure)  continued  from  the  ven- 
tral margin  dorsad  along  the  caudal  surface  of  the  Hver  (Fig. 
259). 

This  growth  of  the  liver  has  now  effected  a  division  of  the  primi- 
tive ventral  mesogastrium  into  two  segments  : 

1.  Ventral  portion,  between  diaphragm  and  liver,  forms  the 
broad  falciform  or  suspensory  ligament  of  the  liver. 

2.  The  dorsal  portion,  between  liver  and  stomach,  forms  the 
lesser  or  gastro-hepatic  omentum. 

The  caudal  free  edge  of  the  ventral  mesogastrium  extends 
between  the  umbilicus  and  the  caudal  surface  of  the  liver,  carrying 
the  umbilical  vein  between  its  layers.  The  growth  of  the  liver 
serves  to  bury  this  free  edge  and  the  contained  vein  in  a  fissure  on 
the  caudal  surface  of  the  liver.  The  same  obtains  in  the  case  of 
the  ductus  venosus  continued  from  the  umbilical  vein  (umbilical 
fissure  and  fissure  of  ductus  venosus  of  adult  liver).  Conse- 
quently the  original  continuity  of  the  broad  ligament  and  lesser 
omentum,  as  parts  of  the  primitive  ventral  mesogastrium,  is  not 
readily  seen  in  the  adult. 

The  broad  ligament  extends  across  the  convex  cephaUc  surface 
of  the  liver  uniting  it  to  the  ventral  abdominal  wall  and  dia- 
phragm, while  its  free  falciform  edge  apparently  stops  at  the  um- 
bilical notch  in  the  ventral  border  of  the  organ.  Actually,  how- 
ever, the  obliterated  vein  is  surrounded   in  the  bottom  of  the 


166  AMATOMY  OF  THE  PERITONEUM. 

fissure,  by  a  peritoneal  fold  which  effects  the  junction  between 
broad  ligament  and  lesser  omentum. 

We  will  see  later  in  what  way  the  permanent  adult  arrange- 
ment of  the  lesser  omentum  is  brought  about.  For  the  present 
we  can  state,  on  the  hand  of  the  schematic  Fig.  273,  that  the  free 
caudal  edge  of  the  falciform  ligament  containing  the  umbilical 
vein,  and  the  free  edge  of  thegastro-hepatic  omentum  form  together 
originally  the  caudal  free  edge  of  the  ventral  mesogastrium,  which 
membrane  becomes  separated,  b}?^  the  growth  of  the  liver,  into 
suspensory  or  broad  ligament  and  lesser  or  gastro-hepatic 
omentum. 

This  primitive  disposition  of  the  ventral  mesogastrium  and  the 
viscera  connected  with  the  same,  is  well  shown  in  some  of  the 
lower  vertebrates  in  whom  the  development  never  proceeds  be- 
yond the  early  mammalian  stages.  Fig.  275  shows  in  profile 
view  from  the  right  side  the  situs  viscerum  and  peritoneum  in 
Iguana  tuherculata}  The  two  dorsal  aortic  roots  are  seen  to  unite 
to  form  the  main  aorta,  which  descends  between  the  layers  of 
the  dorsal  mesentery,  sending  branches  to  the  dorsal  margin  of 
oesophagus  and  stomach.  From  the  opposite  border  of  the  stomach 
the  ventral  mesogastrium  is  derived.  Its  dorsal  segment  (gastro- 
hepatic  omentum)  connects  liver  and  stomach,  carrying  between 
its  layers  the  portal  vessels,  hepatic  artery  and  biliary  duct.  The 
ventral  segment  of  the  membrane,  forming  the  suspensory  or  broad 
ligament,  extends  between  abdominal  wall  and  ventral  surface  of 
the  liver.  Caudad,  the  lesser  omentum  and  the  suspensory  liga- 
ment are  seen  to  have  a  common  concave  falciform  edge. 

The  ventral  abdominal  vein  ascends  between  the  layers  of  the 
suspensory  ligament  and  near  the  liver  becomes  connected  by  a 

^Iguana  tuberculata,  one  of  the  large  lizards  native  of  South  America.  This  animal  forms 
an  excellent  object  for  the  comparative  study  of  the  visceral  and  vascular  anatomy  of  the 
abdomen.  It  possesses  a  well-differentiated  intestinal  tract,  several  coils  of  small  intestine, 
a  well-marked  caecum  and  large  intestine.  The  examination  of  this  or  a  similar  reptilian 
form  is  to  be  highly  recommended.  Iguana  is  easily  obtained  in  any  of  our  large  cities,  as  a 
considerable  number  of  these  animals  are  annually  imported  from  Mexico  and  the  South 
American  states. 


PERITONEAL  RELATIONS  OF  LIVER.  167 

large  branch  with  the  portal  vein.  A  few  smaller  branches  are 
seen  passing  from  the  abdominal  wall  beyond  this  point.  In  this 
reptile,  therefore,  the  permanent  vascular  arrangement  corre- 
sponds to  an  early  human  embryonic  stage. 

The  reptilian  ventral  abdominal  vein  is  the  homologue  of  the 
umbilical  vein  of  the  placentalia.  The  large  branch  passing  to 
the  portal  vein  represents  the  connection  established  in  the  human 
embryo  between  the  umbilical  and  portal  veins.  The  small 
branches,  continuing  cephalad  between  the  mesogastric  layers, 
represent  the  temporary  proximal  remnants  which  in  the  human 
embryo  the  umbilical  veins  form  in  connection  with  abdominal 
walls.  The  permanent  adult  arrangement  of  this  part  of  the 
vascular  system  in  this  animal  corresponds  therefore  to  one  of 
the  stages  of  development  in  the  tiiuman  embryo,  as  previously 
indicated  (cf  p.  149 ;  Figs.  251  and  252). 

PERITONEAL   RELATIONS   OE*   LIVER. 

It  is  well  to  begin  the  study  of  the  peritoneal  connections  of  the 
liver  with  the  consideration  of  the  embryonic  stage  shown  in  Fig. 
273  schematically. 

If  we  imagine  this  embryonic  liver  detached  from  its  connec- 
tions in  such  a  manner  as  to  leave  the  divided  peritoneal  layers 
of  the  ventral  mesogastrium  as  long  as  possible,  and  if  we  regard 
the  preparation  from  behind,  the  appearance  of  the  parts  could 
be  represented  in  Fig.  276.^ 

It  will  of  course  be  seen  that  the  area  of  direct  adhesion  to 
the  diaphragm,  extending  transversely,  would  separate  the  lesser 
omentum  from  the  suspensory  ligament. 

As  is  seen  in  the  transection  (Fig.  274),  the  right  and  left  layers 
of  the  suspensory  ligament,  at  its  attachment  to  the  liver,  turn 
into  the  visceral  peritoneum  investing  the  organ  on  its  ventral 
and  cephalic  surfaces.     Continuing  around  the  borders  of  the 

'  I  am  indebted  to  Dr.  J.  A.  Blake,  former  Assistant  Demonstrator  of  Anatomy  at  Colnra- 
bia  University,  for  the  valuable  suggestion  which  led  to  the  preparation  of  Figs.  276,  277 
and  278  together  with  the  correlated  text. 


168  ANATOMY  OF   THE  PERITONEUM. 

liver  this  visceral  peritoneum  then  invests  in  like  manner  the 
dorsal  or  caudal  surface  directed  toward  the  stomach,  until,  at  the 
region  of  the  future  portal  or  transverse  fissure,  this  visceral  peri- 
toneum becomes  in  turn  continuous  with  the  two  layers  of  the 
lesser  or  gastro-hepatic  omentum.  Consequently  in  the  embry- 
onic detached  liver  the  lines  of  peritoneal  reflection  would  be 
nearly  cruciform,  the  vertical  limb  of  the  cross  being  formed  on 
the  cephalic  surface  by  the  two  layers  of  the  suspensory  ligament, 
while  on  the  caudal  surface  it  is  formed  by  the  layers  of  the  lesser 
omentum.  The  horizontal  arm  of  the  cross  is  formed  by  the 
upper  and  lower  limits  of  the  area  of  diaphagmatic  attach- 
ment, along  which  the  parietal  diaphragmatic  peritoneum  turns 
into  the  visceral  hepatic  investment  (forming  the  two  layers  of  the 
primitive  coronary  ligament).  In  the  liver  shown  thus  sche- 
matically from  behind  we  would  overlook  the  dorsal  and  adjoin- 
ing portions  of  the  cephalic  and  caudal  surfaces  of  the  adult 
human  liver. 

The  primitive  biliary  duct,  portal  vein  and  hepatic  artery  reach 
the  liver  between  the  layers  of  the  lesser  omentum.  The  venae 
revehentes  (hepatic  veins)  reach  the  sinus  venosus  at  the  attach- 
ment of  the  liver  to  the  septum  transversum  (primitive  dia- 
phragm). 

The  first  important  change,  resulting  in  a  rearrangement  of 
these  peritoneal  layers,  is  produced  by  the  connection  of  the 
umbilical  with  the  rudimentary  portal  vein. 

This  junction  occupies  a  relatively  wide  area  on  the  caudal 
surface  of  the  liver,  and  the  layers  of  the  lesser  omentum  are 
separated  somewhat  at  this  point  to  accommodate  the  enlarging 
vascular  structures  between  them.  More  especially  is  this  the 
case  with  the  right  leaf  of  the  primitive  gastro-hepatic  omentum. 
A  species  of  lateral  diverticulum  is  formed  by  this  leaf  so  as  to 
include  the  umbilical  vein  at  its  junction  with  the  portal. 
The  membrane  in  the  region  of  this  diverticulum  turns  its  surfaces 
dorsad  and  ventrad,  and  its  free  edge  toward  the  right  (Fig.  277). 
With  the  gradual  increase  in  the  size  of  the  vessels,  and  with  the 


PERITONEAL  RELATIONS  OF  LIVER.  169 

transverse  position  which  the  rotation  of  the  stomach  imparts  to 
the  opposite  border  of  the  lesser  omentum  attached  to  the  lesser 
curvature,  this  transversely  disposed  portion  gradually^ exceeds  in 
length  and  size  the  part  of  the  original  omentum  enclosing  the 
umbilical  vein.  This  vessel  and  the  investing  peritoneum  be- 
come lodged  in  a  sagittal  depression  on  the  caudal  surface  of  the 
hver  (rudimentary  umbilical  fissure),  while  the  transverse  portion, 
developed  as  indicated,  surrounds  the  structures  connected  with 
the  liver  at  the  future  transverse  or  portal  fissure. 

Schematically  this  rearrangement  of  the  hepatic  peritoneal  lines 
of  reflection  can  be  shown  in  Fig.  278. 

It  will  be  observed  that  in  this  way  a  small  part  of  the  caudal 
surface  of  the  right  lobe  has  become  partially  marked  oiBf  from  the 
remainder  as  a  rudimentary  Spigelian  lobe,  bounded  ventrally  by 
the  transverse  fissure  and  lesser  omentum  attached  to  the  same ; 
to  the  left  by  the  two  layers  of  the  lesser  omentum  containing 
the  ductus  venosus ;  while  the  limit  cephalad  is  afforded  by  the 
reflection  of  peritoneum  from  liver  to  diaphragm,  forming  part  of 
caudal  layer  of  right  coronary  ligament.  To  the  right  this  rudi- 
mentary Spigelian  surface  is  directly  continuous  with  the  rest  of 
the  dorsal  and  caudal  surface  of  the  right  lobe  (Fig.  277). 
Finally  a  definite  right  limit  is  given  to  the  Spigelian  lobe  by  the 
increasing  size  of  the  postcava  and  its  closer  connection  with  the 
liver.  This  vessel  now  assumes  the  position  of  the  main  venous 
trunk  entering  the  heart  from  below. 

This  inclusion  of  the  vena  cava  in  the  fissure  or  fossa  of  that 
name  on  the  dorsal  surface  of  the  liver  affords,  so  to  speak,  the 
vertical  measure  of  the  non-peritoneal  area  of  the  liver  attached 
directly  to  the  diaphragm.  As  the  vein  develops  the  interval 
between  the  two  layers  of  the  right  coronary  ligament  increases, 
producing  the  well-known  large  non-peritoneal  area  on  the  dorsal 
surface  of  the  adult  liver,  which  is  directly  attached  to  the 
diaphragm. 

Immediately  to  the  left  of  the  vena  cava,  however,  the  original 
condition  persists.     The  area  of  direct  diaphragmatic  attachment 


170  ANATO^fY  OF  THE  PERITONEUM. 

is  narrow  and  consequently  the  two  layers  of  the  coronary  liga- 
ment are  close  together  at  this  point.  ^ 

In  this  way  a  species  of  recess  (Spigelian  recess  or  hepatic 
antrum  of  lesser  sac)  is  formed.  A  portion  of  the  dorsal  liver 
surface  lying  just  to  the  left  of  the  vena  cava,  between  it  and  the 
ductus  venosus,  remains  invested  by  peritoneum  which  is  reflected 
from  the  boundaries  of  this  space  to  the  diaphragm.  Thi-s  forms 
the  Spigelian  lobe  (Fig.  278). 

The  lobe  is  bounded  to  the  right  by  the  postcava,  to  the  left 
by  the  reflection  of  the  lesser  omentum  to  the  stomach  along  the 
fissure  for  the  ductus  venosus ;  cephalad  the  boundary  is  formed 
by  the  reflection  of  the  caudal  layer  of  the  coronary  ligament  to 
the  diaphragm. 

The  caudal  boundary  is  afforded  by  the  transverse  position 
which  the  lesser  omentum  has  assumed  in  the  region  of  the  trans- 
verse or  portal  fissure. 

It  will  be  seen  that  the  original  continuity  of  the  Spigelian 
lobe  with  the  caudal  surface  of  the  right  lobe  is  maintained  by 
the  narrow  bridge  of  liver  tissue  connecting  the  caudal  right  angle 
of  the  rectangular  Spigelian  lobe  with  the  right  lobe.  This  nar- 
row isthmus,  situated  between  vena  cava  dorsad  and  the  free  right 
edge  of  lesser  omentum  ventrad,  forms  the  so-called  caudate  lobe. 

Fig.  279  shows  a  human  foetal  liver  at  the  end  of  the  eighth 
month  in  the  view  from  below  and  behind.  The  original  con- 
tinuity of  the  layers  of  the  lesser  omentum,  attached  along  the 
fissure  for  the  ductus  venosus,  with  the  fold  of  the  falciform  liga- 
ment occupying  the  umbilical  fissure  can  still  be  made  out  for  a 
short  distance  beyond  the  left  extremity  of  the  transverse  fissure. 
The  section  of  the  lesser  omentum  which  occupies  the  transverse 

1  It  should  be  remembered  that  in  the  final  adnlt  arrangement  of  the  abdominal  viscera 
the  liver  shifts  relatively  backwards,  so  that  the  diaphragmatic  attachment,  originally  directed 
cephalad,  now  looks  dorsad  and  forms  part  of  the  dorsal  or  "  posterior  "  surface  of  the  ad  alt 
organ.  The  original  ventral  surface  looks  cephalad,  as  well  as  ventrad,  forming  the  convex 
surface  which  in  the  adult  rests  in  contact  with  the  abdominal  wall  and  diaphragmatic 
vault,  while  the  surface  originally  directed  dorsad  toward  the  stomach  finally  in  large  part 
has  an  inclination  caudad  forming  the  "inferior  "  surface  of  human  anatomy. 


PERITONEAL  RELATIONS  OF  LIVER.  171 

fissure  and,  including  the  portal  vein,  hepatic  artery  and  duct 
between  its  layers,  terminates  in  the  free  right  margin,  is  evidently 
derived  by  a  lateral  extension  from  the  right  layer-of  the  primi- 
tive sagittal  lesser  omentum,  whose  original  direction  is  preserved 
along  the  fissure  of  the  ductus  venosus. 

In  Fig.  280  the  lines  of  peritoneal  reflection  on  the  cephalic, 
dorsal  and  caudal  surfaces  of  a  human  foetal  liver  at  term  are 
shown. 

We  can  now  proceed  to  trace  the  reflection  of  the  peritoneum 
from  the  liver  to  adjacent  structures. 

Begin  with  the  caudal  layer  of  the  coronary  ligament  on  the 
extreme  right,  where  fusion  with  the  corresponding  cephalic 
layer  produces  the  right  triangular  ligament.  The  caudal  layer 
of  the  coronary  ligament  proceeds  from  right  to  left  along  the 
caudal  margin  of  the  non-peritoneal  dorsal  diaphragmatic  surface 
of  right  lobe,  being  reflected  along  this  line  from  the  liver  to  the 
adjacent  portions  of  the  diaphragm  and  ventral  surface  of  right 
kidney  and  suprarenal  capsule  (hepato-renal  ligament).  A  small 
cephalic  part  of  ventral  surface  of  right  suprarenal  capsule  lies 
above  this  line  of  reflection,  is  hence  non-peritoneal  and  firmly 
connected  with  the  liver  just  to  the  left  of  entrance  of  vena 
cava  into  the  caval  fissure.  Continuing,  the  caudal  layer  of  the 
coronary  ligament  crosses  the  ventral  surface  of  the  vena  cava 
and  turns,  immediately  to  the  left  of  the  vein,  at  a  right  angle, 
ascending  to  form  the  left  boundary  of  the  Spigelian  recess,  being 
reflected  along  this  line  from  the  left  margin  of  the  caval  fissure 
to  the  pillars  of  the  diaphragm.  Arrived  at  the  opening  of  the 
central  tendon  permitting  passage  of  vena  cava  into  pericardium, 
and  at  the  level  of  the  entrance  of  the  left  hepatic  vein  into  the 
cava,  the  peritoneum  turns  again  at  a  right  angle  and  runs  from 
right  to  left,  forming  the  cephalic  limit  of  the  Spigelian  recess. 
Turning  caudad  along  the  fissure  for  the  ductus  venosus,  as  right 
leaf  of  that  portion  of  the  lesser  omentum  which  is  attached  to  this 
fissure  and  has  preserved  its  sagittal  position,  the  peritoneal  line 
of  reflection  reaches  the  left  extremity  of  the  portal  or  transverse 


172  ANAT03IY   OF  THE  PERITONEUM. 

fissure.  It  now  turns  to  the  right  following  the  fissure  as  the 
dorsal  layer  of  the  transverse  segment  of  the  lesser  omentum,  and 
becomes  continuous,  with  the  formation  of  a  free  right  edge,  with 
the  ventral  layer  of  the  same  membrane,  passing  from  right  to 
left,  the  two  layers  including  between  them  the  structures  enter- 
ing and  leaving  the  liver  at  the  transverse  fissure  (portal  vein, 
hepatic  artery,  duct).  Arriving  at  the  left  extremity  of  the  trans- 
verse fissure  the  ventral  layer  of  the  transverse  segment  of  the 
lesser  omentum — as  we  practically  trace  it  in  the  adult  as  a  free 
membrane — turns  directly  into  the  left  leaf  of  the  sagittal  seg- 
ment attached  along  the  fissure  for  the  ductus  venosus,  and  be- 
comes continuous  along  the  dorsal  border  of  the  left  lobe  with  the 
caudal  layer  of  the  left  coronary  ligament.  This  direct  continuity, 
as  just  stated,  exists  practically  in  the  adult.  From  the  develop- 
ment of  the  membrane,  however,  it  will  be  seen  that  the  ventral 
layer  of  the  transverse  lesser  omentum,  at  the  left  extremity  of 
the  portal  fissure,  becomes  continuous  with  the  right  layer  of  the 
primitive  mesogastrium  enclosing  the  umbilical  vein.  After  sur- 
rounding this  vein  it  is  continued  into  the  left  leaf  of  the  same 
membrane,  which  in  turn  passes  into  the  left  layer  of  the  portion 
attached  along  the  fissure  for  the  ductus  venosus. 

This  original  connection  can  at  times  be  traced  very  clearly  in 
young  specimens  (Fig.  279),  and  occasionally  is  also  still  evident 
in  the  adult  liver. 

Usually,  however,  the  round  ligament  of  the  adult  and  its 
investing  peritoneum  is  buried  so  deeply  in  the  umbilical  fissure, 
or  even  bridged  over  in  part  by  liver  tissue,  that  the  connection 
is  not  evident.  The  ventral  layer  of  the  transverse  omentum  then 
appears  directly  continuous  with  the  left  layer  of  the  sagittal 
omentum  attached  along  the  fissure  for  the  ductus  venosus. 

We  can  sum  up  the  facts  just  considered  as  follows : 

1.  The  rotation  of  the  stomach  from  the  sagittal  into  the  trans* 
verse  position,  and  the  development  of  the  umbilical  and  portal 
veins,  rearrange  the  original  sagittal  plane  of  the  lesser  omentum, 
dividing  it  into  two  districts  : 


PERITONEAL  RELATIONS  OF  LIVER.  173 

(a)  Cephalic  portion,  remaining  in  the  original  sagittal  plane, 
follows  the  fissure  for  the  ductus  venosus.  With  the  incorpora- 
tion of  the  Spigelian  lobe  in  the  adult  dorsal  or  "posterior"  sur- 
face of  the  Hver,  this  segment  of  the  omentum  assumes  a  vertical 
direction,  forming  the  left  boundary  of  the  Spigelian  recess,  being 
reflected  from  the  fissure  for  the  ductus  venosus  to  the  abdominal 
portion  of  the  oesophagus  and  the  part  of  the  lesser  curvature  of 
stomach  adjacent  to  the  cardia. 

(6)  Distal  caudal  portion  of  the  lesser  omentum  is  twisted  later- 
ally and  turned  to  the  right  by  the  change  in  the  position  of  the 
stomach  and  the  development  of  the  structures  connected  with 
the  liver  at  the  transverse  fissure.  It  is  reflected  from  this  fissure 
to  the  distal  part  of  the  lesser  curvature  and  to  the  first  portion 
of  the  duodenum.  This  transverse  segment  of  the  lesser  omentum 
is  a  secondary  derivative  from  the  right  leaf  of  the  primitive 
membrane,  produced  by  the  enlarged  area  for  entrance  of  umbil- 
ical and  portal  veins  at  the  transverse  fissure.  It  lies  ventrad  of 
caudal  border  of  Spigelian  lobe. 

2.  The  distal  segment  of  the  original  omentum  containing  the 
umbilical  vein  (round  ligament),  continues  imbedded  in  the  umbil- 
ical fissure,  to  the  ventral  margin  of  the  liver,  where  it  joins  the 
layers  of  the  suspensory  ligament  passing  over  the  cephalic  surface. 

3.  The  adult  lesser  omentum  at  the  transverse  fissure  may  be 
regarded  as  a  diverticulum  of  the  right  leaf  of  the  primitive 
embryonal  sagittal  omentum. 

With  the  reduction  of  the  umbilical  vein  after  birth  to  form 
the  round  ligament  this  structure  becomes  deeply  buried  in  the 
umbilical  fissure.  The  ventral  and  dorsal  layers  of  the  lesser 
omentum  at  the  transverse  fissure  thus  become  continuous  with 
respectively  the  left  and  right  layers  of  the  second  segment  of  the 
omentum  which  ascends  vertically  along  the  fissure  for  the  ductus 
venosus. 

4.  The  cephalic  layer  of  the  coronary  ligament  (Fig.  280)  re- 
mains practically  in  the  embryonic  condition.  The  adult  convex 
cephalic  surface  of  the  liver  is  traversed  in  the  sagittal  direction 


174  ANATOMY  OF  THE  PERITONEUM. 

by  the  suspensory  ligament  which  connects  it  with  the  abdominal 
surface  of  the  diaphragm,  and  thus  effects  the  division  into  right 
and  left  lobes  on  the  convex  surface.  Arrived  at  the  dorsal 
border  of  this  surface  (junction  of  "superior"  and  "posterior" 
surfaces)  the  right  and  left  leaves  of  the  falciform  ligament  turn 
at  right  angles  into  the  cephalic  layer  of  the  right  and  left  coro- 
nary ligament,  which  at  each  extremity  meet  the  right  and  left 
caudal  layers  to  form  the  triangular  ligaments.  It  will  thus  be 
seen  that  the  apparent  irregularity  in  the  relative  arrangement  of 
the  s.  c.  "upper"  and  "lower"  layers  of  the  coronary  ligaments, 
produced  by  the  Spigelian  recess,  is  only  a  difference  in  the  inter- 
val between  the  two  layers,  caused  by  the  vertical  extent  of  the 
non-peritoneal  direct  diaphragmatic  attachment  of  the  right  lobe 
to  the  right  of  the  vena  cava. 

Comparative  Anatomy  of  Spigelian  Lobe  and  Vena  Cava  in  the  Cat. — The 

lines  of  peritoneal  reflection  in  the  cafs  liver  and  the  arrange- 
ment of  the  Spigelian  lobe  and  recess  are  seen  in  Fig.  281,  taken 
from  a  preparation  hardened  in  situ. 

Compared  with  the  human  liver  it  will  be  noted  that  the  area 
of  diaphragmatic  adhesion  is  much  less  developed.  The  dorsal 
surface  of  the  right  lobe  to  the  right  of  the  postcava  is  peri- 
toneal, there  being  no  extension  laterad  of  the  right  coronary  and 
triangular  ligaments.  The  postcava  enters  the  liver  in  a  special 
prolongation  of  the  liver  substance  (caval  lobe). 

The  boundaries  of  the  Spigelian  recess  and  the  lines  of  attach- 
ment of  the  gastro-hepatic  omentum  correspond  to  the  human 
arrangement. 

RELATION  OF  THE  HEPATIC  PERITONEUM  TO  THE 
"LESSER  SAC." 

Foramen  of  Winslow. — We  have  previously  seen  that  the  rotation 
of  the  stomach  and  the  further  growth  of  the  dorsal  mesogastrium 
lead,  in  the  first  instance,  to  the  formation  of  the  "lesser  peritoneal 
cavity."  This  cavity  is  in  fact  primarily  the  retrogastric  space 
created  by  the  transverse  position  of  the  stomach,  augmented  by 


RELATION  OF  HEPATIC  PERITONEUM  TO   THE  LESSER  SAC.    175 

the  cavity  of  the  omental  bursa  developed  from  the  dorsal  meso- 
gastrium. 

We  have  now  to  consider  the  additional  boundaries  of  this 
space  contributed  by  the  peritoneal  connection  of  the  lesser 
curvature  with  the  liver. 

The  lesser  omentum  follows,  of  course,  along  its  gastric  attach- 
ment to  the  lesser  curvature  the  general  direction  of  the  stomach, 
passing  from  the  cardia  transversely  downwards  and  to  the  right. 
We  distinguish  the  two  layers  of  the  adult  membrane  as  ventral 
and  dorsal,  which  meet  in  the  free  right  edge  and  include  between 
them  the  main  structures  entering  and  leaving  the  liver  at  the 
transverse  fissure,  viz.:  the  portal  vein,  hepatic  artery  and  bile-duct. 

The  lesser  omentum  therefore  prolongs  the  plane  of  the  stomach 
cephalad  towards  the  liver  and  thus  forms  the  continuation  of  the 
ventral  boundary  of  the  lesser  peritoneal  sac.  We  can  now  con- 
sider the  line  of  its  hepatic  attachment  in  the  light  of  the  facts 
previously  adduced,  and  combine  the  same  with  the  line  of  gastric 
attachment  to  the  lesser  curvature.  Fig.  282  shows  the  foetal 
liver  and  stomach  in  their  relative  position  in  the  dorsal  view, 
and  Fig.  283  gives  the  lines  of  the  peritoneal  reflections.  The 
vertical  segment  of  the  omentum,  occupying  the  fissure  for  the 
ductus  venosus,  passes  to  the  cardiac  part  of  the  lesser  curvature, 
its  ventral  layer  covering  the  ventral  and  left  side  of  the  oesopha- 
gus, while  its  dorsal  layer  passes  to  the  dorsal  and  right  side  of 
the  oesophagus  at  its  entrance  into  the  stomach.  The  transverse 
segment  of  the  omentum,  attached  on  the  liver  to  the  portal  or 
transverse  fissure,  accedes  to  the  pyloric  part  of  the  lesser  curva- 
ture. Of  course  the  ventral  and  dorsal  layers  of  the  omentum  are 
continuous  with  the  serous  visceral  investment  of  the  ventral  and 
dorsal  surfaces  of  the  stomach. 

Fig.  284  shows  this  right-angled  course  of  the  lesser  omentum 
at  the  hepatic  line  of  attachment  in  a  preparation  of  the  abdomi- 
nal viscera  hardened  in  situ,  with  the  segment  of  the  stomach 
between  the  cardiac  and  pyloric  orifices  removed.  The  arrow  is 
passed  behind  the  right  free  edge  of  the  lesser  omentum.     This 


176  ANATOMY  OF  THE  PERITONEUM. 

portion  of  the  membrane  is  still  intact,  not  having  been  disturbed 
by  the  removal  of  the  body  of  the  stomach,  and  includes  between 
its  layers  the  structures  connected  with  the  liver  at  the  transverse 
fissure  (duct,  hepatic  artery  and  portal  vein).  The  lesser  omen- 
tum is  seen  to  be  attached  to  the  liver  along  the  transverse  fissure 
(Fig.  284,  A)  and  along  the  fissure  for  the  ductus  venosus  (Fig. 
284,  J?),  constituting  the  transverse  and  vertical  segments  above 
referred  to,  which  pass  into  each  other  at  the  angle  of  junction 
between  the  transverse  fissure  (left  end)  and  the  fissure  for  the 
ductus  venosus  (Fig.  284,  C).  The  caudal  and  left  border  of  the 
Spigelian  lobe  is  exposed  by  the  division  of  the  omentum,  and  the 
extent  of  the  Spigelian  or  hepatic  recess  of  the  lesser  peritoneal 
sac  is  shown.  Fig.  285  shows  the  liver,  stomach  and  lesser  omen- 
tum of  a  Macaque  monkey  hardened  in  situ,  and  demonstrates 
still  more  conclusively  that  the  uniform  curve  of  the  omentum 
along  the  lesser  curvature  of  the  stomach  becomes  a  broken  line 
at  the  hepatic  attachment,  the  angle  being  placed  at  the  left  end 
of  the  transverse  fissure  at  the  point  where  the  same  encounters 
the  fissure  for  the  ductus  venosus. 

In  Fig.  286  finally  the  hardened  abdominal  viscera  of  an  adult 
human  subject  are  shown  in  the  ventral  view  with  the  lesser  omen- 
tum incised.  The  cut  through  the  lesser  omentum  exposes  the 
hepatic  recess  of  the  lesser  peritoneal  cavity  immediately  to  the 
left  of  the  foramen  of  Winslow.  Toward  the  right  free  margin  of 
the  omentum  the  divided  portal  vein,  hepatic  artery  and  duct  are 
seen  between  the  layers  of  the  omentum  imbedded  in  the  pan- 
creas and  coursing  behind  the  first  portion  of  the  duodenum  on 
their  way  to  the  transverse  fissure. 

To  the  left  of  these  structures  the  omental  tuberosity  of  the 
pancreas  projects  above  the  level  of  the  lesser  curvature  under 
cover  of  the  secondary  parietal  peritoneum  forming  the  dorsal 
wall  of  the  lesser  sac,  while  the  lower  edge  of  the  Spigelian  lobe 
appears  in  the  upper  angle  of  the  incision. 

If  we  remember  that  the  liver  is  itself  welded  to  the  diaphragm 
between  the  layers  of  the  coronary  ligament  (Fig.  280),  it  will  be- 


PLATE    CXLV. 


VENTRAL  MESO- 
GASTRIUM 


HEPATIC  ART, 


MESOOUODENUM 


DORSAL  MESOGAS- 
TRIUM  DEVELOPING 
INTO  OMENTAL  BAG 


-   DUODENUM 


Fig.  289. — Stages  iu  the  development  of  the  dorsal  mesogastrium  (omental  bursa) 
and  mesoduodenum  to  show  relation  of  hepatic  artery  to  these  two  segments  of  the 
primitive  common  dorsal  mesentery. 


GREAT  OMENTUM 
TURNED    UP    AND 
DIVIDED     TO      EX- 
POSE   RETRO- 
GASTRIC  SPACE 


HEPATIC   ART. 
PORTAL    VEIN 


PANCREAS 


SMALL    IN- 
TESTINE 


STOMACH 


CORONARY  ART 
AND    VEIN 


Fig.  290. — Abdominal  viscera  of  Nanua  rufa,  brown   coaiti,  with  stomach   turned  up 
and  great  omentum  divided.     (From  a  fresh  dissection.) 


PLATE    CXLVI. 


GASTRO-SPLENIC 

OMENTUM  WITH    A. 

GASTHO-EPIPLOICA 

SINISTRA 


DORSAL  MESOGAS- 
TRIUM  WITH 
SPLENIC    ART. 

PRIMITIVE 

PARIETAL 

PERITONEUM 


i 

t 

■i 

^ 

HI 

k 

s 

P 

« 

^^^^^ 

^^^^ 

STOMACH 


MESOOUOOENUM 
CARRYING   HEPATIC 
ARTERY 


PRIMITIVE 
PARIETAL 
PERITONEUM 


Fig.  291. — Schematic  transection  through  foramen  of  Winslow  before  adhesion  of  dorsal  meso- 
gastrium  and  mesoduodenum  to  parietal  peritoneum. 


J^ 

i  '^AK- 

"^M^^ 

1^  J 

\/      V 

^^v '^ 

.■i 

HEPATIC    ART. 


AREA  OF  ADHESION  BETWEEN 
PRIMITIVE  PARIETAL  PERITO- 
NEUM AND  DORSAL  MESO- 
GASTRIUM 


AREA  OF  ADHESION  BETWEEN 
MESODUODENUM  AND  PRIMI- 
TIVE    PARIETAL     PERITONEUM 


Fig.  292. — The  same  section  after  the  adult  conditions  have  been  established  by  adhesion. 


PLATE    CXLVII. 


BILE-DUCT 


RIGHT    LOBE 
OF    LIVER 


POSTCAVA 
AORTA 


R.    KIDNEY 


FALCIFORM   LIG. 
L.    LOBE  OF  LIVER 


PYLORUS 
STOMACH 


DUODENUM 
PANCREAS 


PORTAL   V. 
HEPATIC    A. 

COMMON    ORIGIN    OF 
HEPATIC      AND       SUP. 
MESENT.   ARTERIES 
INF.  MESENT.  A. 


COMMON   DORSAL 
MESENTERY,  RIGHT 
LEAF 


ILEO-COLIC 
JUNCTION 


Fig.  2y3.--Ab(loiiiiual  viscera  of  TamuiuUa  bhUtata,  the  little  ant-eater,  with  the  intestines 
turned  downward  and  to  the  left.     (From  a  fresh  dissection.) 


I 


PLATE    CXLVIII. 


FORAMEN     OF 
WINSLOW 


HEPATIC    ART 


DIAPHRAGM 


PYLORO- DUODENA! 
JUNCTION 


PANCREAS,   BETWEEN 
LAYERS     OF    STILL 
FREE   MESODUOD- 
ENUM 


FiC4.  294. — Schematic  sagittal  section  through  foraiueii  of  Wiuslow  before  fixation 
of  pancreas  by  adliesiou  of  mesoduodeuum. 


FORAMEN    OF 
WINSLOW 

HEPATIC    ARTERY 


PANCREAS 


DIAPHRAGM 


LESSER    OMENTUM 
'LIG.    HEPATO- 
DUODENALE* 

PYLORO- DUODENAL 
JUNCTION 


Fig.  295. — The  same  section  after  adhesion  of  uiesoduodenuni  and  pancreas.  The 
pancreas  appears  secondarily  retroperitoneal,  after  adhesion  of  ai)posed  surfaces  of  nieso- 
duodenuni  and  primitive  parietal  peritoneum  over  dotted  area,  producing  fixation  of 
dorsal  surface  of  pancreas. 


PLATE   CXLIX. 


QUADRATE    LOBE 


RIGHT    LOBE 

HEPATIC   DUCT 

HEPATIC    ART, 

PORTAL    ' 

CYSTIC   DU 

A.GASTRO-DUODE'-J 

POSTCAVA 

COMMON   BILE-DUCT 


A.    PANCREATICO- 
OUODENALIS  SUP. 


DUODENUM 


POSTCAVA 


L.   LOBE 
L.    GASTRO 
EPIPLOIC 
SPLEEN 

SPIGELIAN 
GASTRIC  A 
SPLENIC  A 
SPLENIC  V 
PANCREAS 
TRAL  SUR 
PANCREAS 
TRAL  MAR 
PANCREAS 
SURFACE 

ART.  PANC 
DUODENAI 

SUP.  MES 
SUP.    MESI 


Fig.  ii96.— Dissection  of  adult  liver,  pancreas,  spleen,  and  duodenum,  with  vessels,  to  show 
structures  concerned  in  the  formatijn  of  the  foramen  of  Winslow.  (Columbia  University,  Study 
Collection.) 


VENTRAL    ME 
GASTRI 


UMBILICAL  V 


FREE     EDGE 

VENTRAL  ME 

GASTR 


HEPATIC   RECESS 
OF    LESSER    SAC 


PANCREAS 


DUODENUM 
DORSAL  MESOGAS- 
TRIUM    FORMING  DOR- 
SAL LAYERS  OF  OMEN- 
TUM    MAJUS 

TRANSV.  MESOCOLON 


TRANSV.  COLON 


Fig.  297.— Schematic  sagittal  section  of  the  ventral  and  dorsal   mesogastria  and 
epiploic  bursa  in  a  human  embryo  of  eight  weeks.     (Modified  from  Kollmann.) 


PLATE    CL. 


FALCIFORM   LIG. 
OF   LIVER 


GASTRO-HEPATIC 
OMENTUM 


DORSAL   MESO- 
GASTRIUM 


PARIETAL 
/       PERITONEUM 
VISCERAL 
PERITONEUM 


STOMACH 

VISCERAL  PERI 
TONEUM     OF 
STOMACH 


Fig.  298. — Transection  of  human  embryo  of  3  cm.,  vertcx-coccygeal  measure. 
(KoUmann.) 


DIAPHRAGM 


STOMACH 


TRANSV.    COLON 


SPLENIC  ART. 
GASTRIC  AND 
HEPATIC    ART. 

PANCREAS 

SUP.    MESENT.    A 

DUODENUM 

TRANSV.    MESOCOLON 
WITH   A.    COLICA    MEDIA 

MESENTERY 
SMALL  INTESTINE 


INF.    MESENT.   ART. 


Fig.  299.— Schematic  sagittal  section  of  abdomen  to  illustrate  the  intestinal  branches 
of  the  abdominal  aorta.  The  gastric  and  hepatic  arteries  are  shoAvn  for  the  sake  of 
convenience  as  arising  together  from  the  coeliac  axis  {li),  hence  the  left  and  right  gastro- 
pancreatic  folds  carrying  these  vessels  appear  fused  at  their  beginning,  separating  the 
henatic  recess  of  the  lesser  peritoneal  sac  (A)  from  the  cavity  of  the  omental  bursa  (C). 


PLATE   CLT. 


PANCREATIC 
DUCT 


COMMON 
BILE-DUCT 


DIVERTICU- 
LUM VATERI 


Fig.  301. — Duodenum,  with  entrance  of  pancreatic 
and  biliary  ducts  and  well-developed  diverticulum  Vateri 
in  the  cassowary,  Casuarius  eastiarius.  (Columbia  Uni- 
versity Museum,    Xo.  1821.) 


PLATE    CLII. 


Fio.  300. — Small  intestine  of  polar 
bear,  Ursus  maritimus.  Mucous  surface. 
(Columbia  University  Museum,  No.  782.) 


FiCi.  302. — Mucous  membrane  of  mid- 
gut of  Boa  constrictor.  (Columbia  Univer- 
sity Museum,  No.  1837.) 


RELATION  OF  HEPATIC  PERITONEUM  TO   THE  LESSER  SAC     177 

come  apparent  that  the  serous  surface  of  the  Spigelian  lobe  forms 
part  of  the  ventral  wall  of  a  peritoneal  recess  situated  behind  the 
lesser  omentum,  between  this  membrane  and  the  -diaphragm. 
Access  to  this  recess,  without  the  division  of  peritoneal  layers,  can 
only  be  obtained  by  passing  from  right  to  left,  along  the  caudate 
lobe,  between  the  vena  cava  behind,  covered  by  parietal  peri- 
toneum, and  the  free  right  edge  of  the  lesser  omentum  in  front. 
(In  the  reverse  direction  of  the  arrow  shown  in  Fig.  284.)  This 
hepatic  or  Spigelian  recess  of  the  lesser  peritoneal  cavity  has  cate- 
gorically the  following  boundaries  (Figs.  282  and  283) : 

Dorsal :  Parietal  peritoneum,  reflected  along  the  line  cd,  from 
the  caudal  layer  of  the  coronary  ligament  to  the  diaphragm. 

Ventral :  Visceral  peritoneum  investing  the  Spigelian  lobe  and 
the  gastro-hepatic  omentum. 

Right :  Reflection  of  peritoneum  along  the  line  de  (caval  fis- 
sure) to  become  the  parietal  peritoneum  covering  the  diaphragm. 

Left :  Right  layer  of  lesser  omentum,  reflected  along  the  fissure 
for  the  ductus  venosus  (cb)  to  the  cardiac  portion  of  the  lesser 
curvature,  continuous  with  the  dorsal  layer  of  the  lesser  omen- 
tum reflected  from  the  transverse  fissure  to  the  pyloric  segment  of 
the  lesser  curvature  (ab). 

We  will  presently  see  that  certain  relations  of  the  vessels  con- 
nected with  the  liver  at  the  transverse  fissure  and  of  the  duo- 
denum prevent  the  finger,  when  passed  from  right  to  left  behind 
the  free  right  edge  of  the  lesser  omentum  and  along  the  caudate 
lobe  of  the  liver,  from  proceeding  downward  at  this  point.  A 
narrow  channel  of  communication  is  thus  formed  between  the 
Spigelian  recess  and  rest  of  the  lesser  sac  on  the  one  hand,  and  the 
general  greater  peritoneal  cavity  on  the  other.  This  channel  is 
the  so-called  foramen  of  Winslow. 

Having  once  passed  this  narrow  space  the  finger  will  be  in 
the  Spigelian  recess  and  can  palpate  its  boundaries.  Further 
progress  cephalad  and  to  the  right  is  barred  by  the  diaphragmatic 
adhesions  of  the  liver  just  detailed.  But  in  the  direction  down- 
(Ward  behind  the  lesser  omentum  and  along  the  dorsal  surface  of 

12 


178  ANATOMY  OF  THE  PERITONEUM. 

the  stomach,  as  well  as  to  the  left  toward  the  spleen  the  excursion 
is  limited  only  by  the  length  of  the  examining  finger. 

After  opening  the  abdominal  cavity  of  the  human  adult,  elevat- 
ing the  liver  and  depressing  the  stomach,  the  hepatic  attachment 
of  the  lesser  omentum  can  be  traced  as  already  described.  It  will 
then  be  observed  that  the  gastric  attachment  of  the  membrane 
lies  in  one  plane  following  the  lesser  curvature  while  the  hepatic 
attachment  forms  a  broken  line,  with  the  angle  situated  at  the 
left  extremity  of  the  transverse  fissure.  The  vertical  segment  of 
the  hepatic  attachment,  occupying  the  fissure  for  the  ductus 
venosus,  turns  at  this  angle  into  the  transverse  segment  which 
follows  the  transverse  fissure  to  its  right  extremity  where  the  two 
layers  pass  into  each  other  around  the  right  free  omental  margin 
(hepato-duodenal  ligament).  Consequently  we  overlook,  in  an 
abdominal  cavity  thus  exposed,  the  entire  caudal  surface  of  the 
liver,  including  the  caudal  surfaces  of  right,  left,  and  quadrate 
lobes.  The  junction  of  right  and  caudate  lobes  can  be  seen 
between  vena  cava  and  right  edge  of  the  omentum,  or  rather,  it 
can  be  felt  at  this  point.  But  the  Spigelian  lobe,  turning  its  sur- 
face dorsad  against  the  parietal  peritoneum  covering  the  dia- 
phragm, forms  part  of  the  "  posterior  "  liver  surface  and  is  not 
visible,  although — as  just  stated,  it  can  be  palpated  by  passing 
the  finger  through  the  foramen  of  Winslow.  The  Spigelian  lobe 
cannot  be  overlooked  in  its  entire  extent  until  the  liver  is  removed 
from  the  body  and  regarded  from  behind.  The  caudal  edge  (con- 
tinuation of  its  right  angle  into  the  caudate  lobe  and  papillary 
tubercle)  can  be  seen  by  tearing  through  the  layers  of  the  lesser 
omentum  and  Hfting  the  liver  up  forcibly  (Fig.  286). 

Caudal  Boundary  of  Foramen  of  Winslow. — We  have  above  re- 
ferred to  the  fact  that  the  finger  introduced  through  the  foramen 
of  Winslow  meets  in  this  canal  with  resistance  if  an  attempt  is 
made  to  pass  downwards.  After  passing  this  constricting  point 
the  free  excursion  into  the  Spigelian  recess  and  behind  the  omen- 
tum and  stomach  and  toward  the  spleen  can  be  performed. 

In  considering  the  elements  which  produce  this  narrowing  of 


CAUDAL  BOUNDARY  OF  FORAMEN  OF  WINSLOW.  179 

the  communication  between  the  two  peritoneal  sacs  at  the  foramen 
of  Winslow  we  have  to  deal  with  two  factors,  one  primary  and 
constant,  the  other  secondary  and  inconstant.  

1.  The  first  of  these  is  afforded  by  the  arrangement  of  the 
arterial  vessel  supplying  the  liver.  The  hepatic  artery  is  a 
branch  of  the  coeliac  axis,  furnishing  arterial  blood  to  the  liver 
tissues  and  supplying,  in  addition,  branches  to  the  stomach,  duo- 
denum and  pancreas. 

This  vessel  is,  of  course,  placed  primarily,  like  all  other  arterial 
branches  supplying  the  alimentary  tract,  between  the  layers  of 
the  primitive  dorsal  mesentery.  Originally  the  vessel  supplies 
the  distal  (pyloric)  portion  of  the  stomach  along  its  dorsal  at- 
tached border  (subsequently  the  greater  curvature)  corresponding 
to  the  adult  gastro-epiploica  dextra  of  the  hepatic  (gastro- 
duodenalis). 

It  likewise  gives  branches  to  the  adjacent  pyloric  portion  of  the 
duodenum  and  the  pancreas,  as  that  gland  develops  from  the  intes- 
tine, corresponding  to  the  adult  superior  pancreatico-duodenal 
branch,  and  to  the  ventral  border  (lesser  curvature)  of  stomach, 
corresponding  to  the  adult  pyloric  branch  of  the  hepatic. 

With  the  development  of  the  liver  from  the  duodenum  arterial 
branches  derived  from  this  primitive  gastro-duodenal  vessel  pass 
to  the  sprouting  hepatic  cylinders  by  continuing  around  the  duo- 
denum, beneath  its  serous  investment,  to  reach  the  interval  be- 
tween the  two  layers  of  the  ventral  mesogastrium,  in  which  the 
liver  develops,  near  the  free  margin  of  this  membrane. 

After  the  rotation,  which  turns  the  right  side  of  the  stomach, 
duodenum  and  mesoduodenum  dorsad,  the  branch  which  passes 
over  the  dorsal  surface  of  the  duodenum  to  reach  the  liver  be- 
comes more  favorably  situated  and  develops  into  the  main  hepatic 
artery  which  reaches  the  liver  at  the  transverse  fissure  between 
the  folds  of  the  lesser  omentum.  The  original  right  side  of  the 
duodenum,  now  turned  dorsad,  adheres  to  the  parietal  perito- 
neum. The  hepatic  artery  which  reached  the  liver  by  passing 
over  this  surface  of  the  duodenum,  beneath  its  visceral  serous  cover- 


180  .  ANATOMY  OF  THE  PERITONEUM. 

ing,  becomes  imbedded  in  connective  tissue  by  the  adhesion  of  the 
visceral  duodenal  and  the  primitive  parietal  peritoneum.  Hence 
in  the  adult  the  hepatic  artery  courses  imbedded  in  the  connective 
tissue  which  binds  the  duodenum  to  the  abdominal  background 
to  reach  the  interval  between  the  two  omental  layers  which  carry 
it  to  the  transverse  fissure. 

The  hepatic  artery,  therefore,  derived  from  one  of  the  primi- 
tive intestinal  branches  (gastro-duodenal)  is,  notwithstanding  its 
hidden  position  in  the  adult,  originally  situated  between  the  layers 
of  the  free  primitive  dorsal  mesogastrium. 

It  now  becomes  necessary  to  regard  the  development  of  the 
great  omentum  from  the  primitive  dorsal  mesogastrium  in  re- 
lation to  this  course  of  the  hepatic  artery.  We  have  seen  that 
the  great  omentum  and  the  cavity  of  the  omental  bursa  is  pro- 
duced by  the  extension  of  the  dorsal  mesogastrium  to  the  left  and 
caudad,  subsequent  to  the  rotation  of  the  stomach.  The  splenic 
artery  and  the  left  gastro-epiploic  branch  pass  from  the  coeliac 
axis  to  the  left  between  the  layers  of  the  mesogastrium,  as  previ- 
ously seen  (Figs.  291  and  292). 

The  hepatic  artery,  however,  is  so  to  speak  placed  on  the  border 
line  between  the  portion  of  the  primitive  mesentery  which,  as 
dorsal  mesogastrium,  is  to  turn  to  the  left  and  caudad  to  form  the 
great  omentum,  and  the  portion  which,  as  mesoduodenum,  turns 
to  the  right  and  passes  to  the  duodenal  loop  (Fig.  287). 

In  the  further  course  of  development  the  dorsal  mesogastrium 
grows  more  and  more,  forming  the  omental  bag,  while  the  meso- 
duodenum on  the  other  hand  becomes  anchored  early  and  obliter- 
ated as  a  free  membrane  by  adhesion  of  its  original  right  layer 
to  the  primitive  parietal  peritoneum.  The  hepatic  artery  runs  on 
the  line  dividing  these  two  different  mesenteric  segments.  We  can 
imagine,  so  to  speak,  that  the  redundant  growth  of  the  omentum 
to  the  left  and  caudad,  takes  place  over  the  hepatic  artery  as  a 
resistant  support  (Figs.  288  and  289).  Cephalad  of  the  hepatic 
artery  is  the  developing  omentum,  caudad  of  the  vessel  the  meso- 
duodenum.    The  artery  follows  the  cephalic  limit  of  the  meso- 


PANCREATICO-QASTRIO  FOLDS.  181 

duodenum  and  becomes,  aa  stated,  adherent  to  the  abdominal 
background  in  the  segment  between  its  origin  from  the  coeUac 
axis  and  the  point  where,  after  having  crossed  the  dorsal  surface 
of  the  duodenum,  it  enters  the  right  edge  of  the  lesser  omentum 
on  its  way  to  the  liver. 

Pancreatico-gastric  Folds. — If  we  open  the  lesser  peritoneal  cavity 
by  dividing  the  gastro-hepatic  omentum  and  look  into  the  back- 
ground of  the  retro-omental  space,  we  will  see  a  fold  of  the 
secondary  lining  parietal  peritoneum  (derived  from  the  mesogas- 
trium),  which  can  be  traded  from  the  cephalic  border  of  the  pan- 
creas to  the  pyloric  extremity  of  the  stomach.  This  fold  carries 
the  hepatic  artery  to  the  lesser  omentum  behind  the  first  portion 
of  the  duodenum,  and  is  called  the  right  or  main  pancreatico- 
gastric  fold.  A  similar  fold,  further  to  the  left,  carries  in  a  like 
manner  the  coronary  artery  of  the  stomach  to  the  cardiac  end  of 
the  lesser  curvature.  This  fold  forms  the  left  or  secondary  pan- 
creatico-gastric  fold.  Between  the  two  folds  the  caudal  margin 
of  the  Spigelian  lobe  projects  into  the  lesser  cavity. 

The  appearance  of  the  two  pancreatico-gastric  folds  in  the 
adult  human  subject  is  well  seen  in  Fig.  284. 

Fig.  290  shows  the  abdominal  cavity  of  Nasua  rufa,  with  great 
omentum  divided  to  bring  into  view  the  vessels  passing  from 
coeliac  axis  to  liver  and  stomach  and  elevating  the  retrogastric 
parietal  peritoneum  to  produce  the  pancreatico-gastric  folds. 

(The  course  of  the  hepatic  artery  from  coeliac  axis  to  liver  in 
the  dorsal  view  in  the  cat  is  seen  in  Fig.  223.) 

Figs.  291  and  292  represent  schematically  cross-sections  directly 
through  the  foramen  of  Winslow,  showing  the  method  by  means 
of  which  the  hepatic  artery  reaches  the  upper  border  of  the  duo- 
denum and  the  effect  of  the  adhesion  of  duodenum  and  meso- 
duodenum  upon  the  disposition  of  the  vessel. 

The  coronary  artery,  like  the  splenic,  is  at  first  situated  between 
the  layers  of  the  dorsal  mesogastriura  (vertebro-splenic  segment). 
Like  the  splenic  the  coronary  artery  becomes  anchored  to  the 
abdominal  background  and  placed  secondarily  behind  the  parietal 


I 


182  ANATOMY  OF  THE  PERITONEUM. 

peritoneum  of  the  lesser  sac  by  the  adhesion  of  this  mesogastric 
segment  to  the  primitive  parietal  peritoneum.  To  reach  the 
lesser  curvature  at  the  cardia  and  to  run  thence  from  left  to  right 
along  the  lesser  curvature  between  the  layers  of  the  gastro-hepatic 
omentum,  the  vessel  raises  the  investing  parietal  peritoneum 
(originally  the  right  leaf  of  the  dorsal  mesogastrium)  into  a  cres- 
centic  fold,  extending  between  its  origin  from  the  cceliac  axis  at 
cephalic  margin  of  pancreas  and  the  beginning  of  the  lesser 
curvature  of  the  stomach.  Hence  this  fold  is  called  the  left  pan- 
creatico-gastric  fold.     (Seen  well  in  Fig.  284.) 

In  the  next  place  it  must  be  borne  in  mind  that  the  relation  of 
the  primitive  hepatic  artery  to  the  vascular  supply  of  the  stomach, 
pancreas  and  duodenum  produces  a  permanent  shortening  of  the 
primitive  mesentery  at  this  point.  This  result  is  indicated  in  the 
schematic  figures  287,  288  and  289. 

In  the  original  condition  the  dorsal  mesentery,  passing  to  a 
practically  straight  intestinal  tube,  is  of  uniform  sagittal  measure 
(Fig.  287). 

As  development  proceeds,  and  as  the  liver  grows  from  the 
duodenum,  the  hepatic  artery  develops  from  the  primitive  pyloric 
vessel  as  above  indicated.  This  vessel,  assuming  greater  impor- 
tance with  the  rapid  growth  of  the  liver,  is  not  lengthened  out  as 
happens  with  the  remaining  purely  intestinal  branches  which 
follow  the  increase  in  the  length  of  the  intestinal  canal.  The 
hepatic  artery,  therefore,  will  mark  the  point  where  the  original 
short  sagittal  extent  of  the  primitive  mesentery  will  tend  to  be 
preserved.  Cephalad  of  this  point  the  dorsal  mesogastrium  grows 
out  into  the  great  omentum  (Figs.  288  and  289) ;  caudad  of  the 
same  point  the  membrane,  in  following  the  development  of  the 
intestine,  becomes  drawn  out  into  the  permanent  mesentery  and 
mesocolon. 

The  hepatic  artery,  in  addition,  marks  the  cephalic  limit  of 
the  adhesion  which  anchors  the  duodenum  and  mesoduodenum 
to  the  parietal  peritoneum.  Consequently  in  the  adult  the  vessel 
courses  in  as  direct  a  manner  as  possible,  taking  the  shortest  course 


HEPATIC  ARTERY.  183 

from  the  coeliac  axis  to  the  liver,  passing  dorsad  of  the  duo- 
denum and  giving  what  now  appear  as  secondary  branches  to 
supply  the  intestine,  the  stomach  and  pancreas  (pyloric  and 
gastro-duodenal  arteries  (pancreatico-duod.  superior  and  gastro- 
epiploica  dextra)). 

Even  if  no  fixation  of  the  duodenum  and  mesoduodenum 
takes  place  this  course  of  the  hepatic  artery  will  produce  a  con- 
stricted passage  between  the  liver  (caudate  lobe)  cephalad,  abdom- 
inal parietes  and  aorta  dorsad,  lesser  omentum  and  pyloric  duo- 
denum ventrad,  and  hepatic  artery  caudad.  This  passage  leading 
from  the  general  peritoneal  cavity  into  the  retrogastric  space  is  the 
primitive  foramen  of  Winslow.  This  condition  is  well  represented 
in  the  abdominal  cavity  of  some  of  the  lower  mammalia,  in 
which  duodenum  and  mesoduodenum  remain  permanently  free. 

Fig.  292  shows  a  view  of  the  abdominal  cavity  from  the  right 
side  in  a  specimen  of  the  ant-eater,  Tamandua  bivittata. 

The  right  kidney  is  seen  in  the  background,  covered  by  the 
parietal  peritoneum.  The  duodenum  and  mesoduodenum  are 
free  and  can  be  turned  toward  the  median  line.  The  opening  of 
the  foramen  of  Winslow  leading  into  the  retrogastric  space  is  seen 
between  the  liver  cephalad,  kidney  and  vena  cava  doread,  lesser 
omentum  and  pyloric  extremity  of  the  stomach  ventrad,  and  a 
fold  of  peritoneum  carrying  the  hepatic  artery  caudad.  Exactly 
similar  conditions  prevail  in  the  cat  and  in  many  other  mammals. 

It  will  be  seen  in  all  these  instances  that  neither  portal  vein 
nor  bile-ducts  limit  the  foramen  caudad.  These  structures  can  be 
lifted  up  and  turned  toward  the  median  line  with  the  free  duo- 
denum and  mesoduodenum.  But  the  hepatic  artery  must  pass 
to  the  liver  from  the  retroperitoneal  cceliac  axis.  In  doing  this 
the  vessel  traverses  the  cephalic  border  of  the  pancreas,  and  the 
pyloric  extremity  of  the  stomach  and  duodenum,  to  reach  the 
lesser  omentum  which  conveys  it  to  the  liver. 

Consequently  there  must  always  be  a  narrow  peritoneal  neck 
between  the  liver  cephalad,  aorta  dorsad,  hepatic  artery  caudad, 
and  pyloric  extremity  of  stomach  and  duodenum  together  with 


184  ANATOMY   OF  THE  PERITONEUM. 

the  lesser  omentum  ventrad.  It  should  be  remembered  that  the 
vessel  which  extends  after  the  development  of  the  Hver  into  the 
lesser  omentum  as  the  hepatic  artery,  was  originally  destined  for 
the  supply  of  these  latter  structures.  In  the  adult  these  primary 
embryonic  terminal  branches  to  the  intestine  appear  as  secondary 
branches  derived  from  the  hepatic  as  the  main  vessel.  Their 
origin,  however,  serves  to  keep  the  beginning  of  the  small  intes- 
tine in  comparatively  close  connection  with  the  hepatic  artery 
which  courses  over  the  dorsal  surface  of  the  duodenum  to  reach 
the  liver.  The  narrow  space  thus  left  between  aorta,  hepatic 
artery,  duodenum,  lesser  omentum  and  liver  forms  the  frame- 
work of  the  foramen  of  Winslow  and  appears  always  as  a  confined 
and  narrow  channel.  This  relation  is  shown  in  the  accompany- 
ing schematic  Figs.  294  and  295  which  represent  a  sagittal  section 
through  the  foramen.  This  primitive  foramen  is  thus  bounded 
cephalad  by  the  liver  (caudate  lobe,  connecting  Spigelian  and  right 
lobes),  ventrad  by  the  first  portion  of  the  duodenum  and  the 
lesser  omentum,  with  hepatic  artery  behind  the  intestine  and 
between  the  omental  layers;  dorsad  by  the  abdominal  back- 
ground and  large  retroperitoneal  vessels,  and  caudad  by  the 
coeliac  axis  and  beginning  of  the  hepatic  artery. 

2.  In  the  forms  which  possess  in  the  adult  an  adherent  duo- 
denum and  mesoduodenum,  as  in  man,  the  foramen  of  Winslow 
obtains  a  secondary  caudal  limit  by  the  agglutination  of  the 
descending  duodenum  and  the  parietal  prerenal  peritoneum. 
This  is  the  secondary  and  inconstant  factor  referred  to  above  in 
the  caudal  boundary  of  the  foramen.  The  result  of  this  anchor- 
ing of  duodenum  and  mesoduodenum  is  to  bring  the  margin  of 
the  foramen  further  to  the  right  and  to  bury  the  hepatic  artery 
still  further  from  view.  Thus  in  the  adult  human  subject  the 
structures  bounding  the  foramen  at  the  margin  of  the  entrance 
into  the  narrow  channel  would  be  above  caudate  lobe  of  liver, 
behind  postcava,  below  duodenum  adherent  to  ventral  sur- 
face of  right  kidney,  in  front  first  portion  of  duodenum  and 
lesser  omentum.     The  hepatic  artery  will  be  felt  on  introducing 


STRUCTURES  BOUNDING  FORAMEN  OF  WINSLOW.  185 

the  finger  through  the  foramen  in  its  original  position,  but  it  will 
be  seen  that  the  actual  boundaries  of  the  foramen  have  been 
moved  so  to  speak  a  little  further  to  the  right  by  the"  duodenal 
adhesion. 

Fig.  296  shows  a  complete  dissection  of  the  adult  human  viscera 
and  vessels  concerned  in  the  formation  of  the  foramen,  hardened 
in  situ. 

The  stomach  is  removed,  dividing  of  course  the  coronary  artery 
and  vein  and  the  left  gastro-epiploic  artery.  The  portal  vein, 
hepatic  artery  and  bile-duct  are  seen  entering  and  leaving  the 
liver  at  the  transverse  fissure.  Behind  them  and  to  the  right  the 
vena  cava  enters  the  liver.  The  hepatic  artery  distributes  its  pan- 
creatico-duodenal  branches  to  the  duodenum  and  pancreas.  The 
left  angle  of  the  Spigelian  lobe  and  the  fissure  for  the  ductus 
venosus  appear  to  the  left  of  the  portal  vein  and  hepatic  artery. 
The  right  angle  of  the  Spigelian  lobe  and  its  continuation  into 
the  right  lobe  by  means  of  the  caudate  lobe  is  hidden  by  the 
structures  occupying  the  transverse  fissure.  We  would  enter  the 
beginning  of  the  foramen  of  Winslow  by  passing  between  the 
vena  cava  behind,  the  structures  in  the  transverse  fissure  (portal 
vein,  hepatic  lartery  and  duct)  in  front,  caudate  lobe  of  liver 
above  and  duodenum  below,  the  latter  in  the  undisturbed  con- 
dition of  the  parts  adherent  to  the  right  kidney.  Continuing  to 
the  left  the  finger  would  pass  between  aorta  behind,  coeliac  axis 
and  hepatic  artery  below  and  in  front,  and  liver  above.  These 
structures  bound  the  permanent  and  primary  narrow  channel 
of  communication  between  the  retrogastric  or  lesser  peritoneal 
space  and  the  general  peritoneal  cavity,  which  exists  even  if  a  free 
duodenum  and  mesoduodenum  allow  us  to  lift  the  intestine  away 
from  vena  cava  and  right  kidney. 

The  main  facts  pertaining  to  the  structure  of  the  lesser  peri- 
toneal sac  and  its  connection  with  the  greater  peritoneal  cavity  by 
means  of  the  foramen  of  Winslow  may  be  summed  up  as  follows  : 

The  mesogastrium  as  a  whole,  expanding  originally  in  the 
sagittal  plane  in  a  fan-shaped   manner  between  the  vertebral 


186  ANATOMY  OF  THE.   PERITONEUM. 

column  and  the  ventral  abdominal  wall,  from  the  level  of  the 
umbilicus  to  the  septum  transversum  (diaphragm),  divides  the 
cephalic  part  of  the  abdominal  cavity  into  a  symmetrical  right 
and  left  half 

Figs.  172  and  273  represent  the  membrane  as  seen  in  a  profile 
view  from  the  left  side.  We  distinguish  the  segment  dorsad  of  the 
stomach  as  the  dorsal  mesogastrium,  directly  continuous  with  the 
remaining  segments  of  the  common  primitive  dorsal  mesentery, 
while  the  portion  ventrad  of  the  stomach  forms  the  ventral  meso- 
gastrium in  which  the  liver  develops.  The  segment  of  the  ven- 
tral mesogastrium  between  liver  and  stomach  becomes  the  lesser 
or  gastro-hepatic  omentum,  while  that  between  liver  and  ventral 
abdominal  wall  forms  the  falciform  or  suspensory  ligament. 

A  transection,  showing  the  dorsal  and  ventral  mesogastrium  at 
the  level  of  the  fundus  of  the  stomach,  is  given  in  Fig.  298.  The 
mesogastria  are  here  seen  to  be  short,  while  in  the  schematic  Figs. 
291  and  292  the  membrane  is,  for  the  sake  of  distinctness,  repre- 
sented as  being  of  considerable  extent. 

The  ventral  mesogastrium  surrounding  the  liver  and  stomach 
extends  caudad  to  include  the  first  portion  of  the  duodenum. 
Beyond  this  point  it  terminates  in  a  thickened  free  edge  which 
includes  the  umbilical  vein.  This  vein  extends  from  the  umbili- 
cus to  the  transverse  fissure  of  the  liver  (Fig.  297),  Ijang  within 
the  umbilical  fissure  on  the  caudal  surface  of  the  gland. 

At  the  point  where  the  vein  enters  the  liver  the  thickened 
margin  of  the  ventral  mesogastrium  is  continued,  as  ligamentum 
hepato-duodenale,  to  the  upper  part  of  the  duodenum  and  forms 
the  ventral  boundary  of  the  foramen  of  Winslow.  Between 
the  layers  of  the  mesogastrium  which  meet  in  this  margin  are 
situated  the  portal  vein,  biliary  duct  and  hepatic  artery,  together 
with  the  nerves  and  lymphatics  of  the  liver. 

The  mesogastrium  originally  divided  the  abdominal  cavity 
between  umbilicus  and  diaphragm  into  symmetrical  right  and 
left  halves  of  equal  size  and  extent.  This  early  symmetrical 
arrangement  becomes  disturbed  about  the  seventh  week  by  the 


SUMMAR  Y  CONNECTION  BETWEEN  LESSER  AND  OREA TER  SA CS.     1 87 

rotation  of  the  stomach  and  the  resulting  altered  course  of  the 
mesogastrium,  which  render  the  two  original  equal  halves  of  the 
abdominal  cavity  unequal  and  asymmetrical.  The  original 
right  half  becomes  placed  behind  the  stomach  and  is  converted 
into  a  blind  sac  with  its  opening  directed  to  the  right. 

The  communication  of  the  general  abdominal  cavity  with  the 
retrogastric  space  by  means  of  this  channel  is  still  wide  in  the 
embryo,  but  gradually  becomes  narrowed  in  the  course  of  further 
development  to  form  the  foramen  of  Winslow.  This  opening  is 
situated  between  the  hepato-duodenal  ligament  and  the  parietal 
peritoneum  covering  the  vena  cava.  It  is  constricted  from  below 
by  the  curve  of  the  hepatic  artery  as  this  vessel  passes  from  the 
cceliac  axis  to  reach  the  liver  at  the  transverse  fissure  between  the 
layers  of  the  lesser  omentum. 

The  earlier  developmental  stages  of  the  higher  mammalian 
embryos  are  in  general  well  illustrated  by  the  permanent  adult 
conditions  found  in  some  of  the  lower  vertebrates,  in  which 
development  does  not  proceed  beyond  the  primitive  condition. 

In  reptiles,  birds  and  mammals  the  epiploic  bursa  is  generally 
formed,  while  in  amphibia  the  dorsal  mesogastrium  is  very  short 
and  connects  the  stomach  directly  to  the  dorsal  midline  of  the 
abdominal  cavity  without  forming  the  sac-like  extension  of  the 
great  omentum. 

The  dorsal  mesogastrium  with  the  stomach,  and  the  ventral 
mesogastrium  including  the  liver  between  its  layers,  divides  in 
these  animals  the  cephalic  part  of  the  body  cavity  into  two 
halves,  corresponding  to  the  earlier  embryonic  stages  in  man  and 
in  the  higher  mammalia. 

The  foramen  of  Winslow  of  the  higher  forms  appears  in  the 
lower  vertebrates  as  the  wide-open  space  leading  from  below  into 
the  right  half  of  the  ccelom  cavity.  The  dorsal  mesogastrium 
remains  short,  not  forming  the  pouch-like  extension  of  the  great 
omentum.  The  stomach  retains  more  or  less  its  primitive  vertical 
position  without  rotation  or  elevation  of  the  pyloric  extremity,  and 
the  intestinal  canal  is  simple,  short  and  comparatively  straight. 


I 


PART  III. 

LARGE  AND  SMALL  INTESTINE,  ILEO-COLIC 
JUNCTION  AND  C^CUM. 

In  considering  the  anatomy  of  the  human  caecum  and  vermi- 
form appendix  many  structural  conditions  are  encountered  which 
can  only  be  correctly  appreciated  in  the  light  of  the  phj^siology 
of  the  digestive  tract.  The  alimentary  canal  as  a  whole  affords 
one  of  the  most  striking  examples  of  the  adaptation  of  structure 
to  function.  The  constant  renewal  of  the  tissues  of  the  body  by 
the  absorption  of  nutritive  material,  the  necessary  concomitant 
egestion  of  undigestible  remnants,  the  variety  in  the  quantity 
and  character  of  the  food  habitually  taken,  all  serve  to  explain 
why  the  alimentary  canal  responds  structurally  in  individual 
forms  so  completely  to  the  physiological  demands  made  upon  it. 
This  will  become  especially  evident  if  we  extend  our  observations 
to  include,  in  addition  to  man,  a  review  of  the  corresponding 
structures  in  representative  types  of  the  lower  vertebrates.  More- 
over the  human  caecum  and  appendix  are  in  part  rudimentary 
structures,  representing  a  portion  of  the  alimentary  tract  which, 
in  accordance  with  altered  conditions  of  food  supply  and  nutri- 
tion, has  lost  its  original  functional  significance  to  the  organism 
and  which  consequently  exhibits  the  wide  range  of  structural 
variation  which  characterizes  the  majority  of  rudimentary  and 
vestigial  organs. 

The  vermiform  process  of  man  and  the  higher  primates  is  thus 
one  of  several  indications  given  in  the  structure  of  the  alimentary 
canal  (the  character  of  the  dentition  is  another  example)  which 
suggests  that  at  one  phylogenetic  period  the  forms  composing  the 
order  or  their  immediate  ancestors  were  largely  or  entirely  herbi- 
vorous, and  hence  possessed  a  more  extensively  developed  csecal 
apparatus  than  their  omnivorous  descendants  of  to-day.     In  ap- 

189 


190  LARGE  AND  SMALL  INTESTINE. 

preaching,  therefore,  the  study  of  the  human  caecum  and  appen- 
dix we  will  at  once  meet  with  conditions  which  call  for  the 
simultaneous  physiological  and  morphological  consideration  of 
the  adjacent  small  and  large  intestine. 

Again  many  of  the  structural  peculiarities  which  characterize 
the  human  csecal  apparatus  can  only  be  correctly  valued  by 
comparison  with  the  corresponding  parts  in  the  lower  verte- 
brates. Our  inquiry  will,  therefore,  most  profitably  include  the 
following  subdivisions  of  the  subject : 

I.  General  review  of  the  functional  and  structural  characters 
of  the  vertebrate  large  and  small  intestine. 

II.  Systematic  consideration  of  the  ileo-colic  junction  and  the 
connected  structures  in  the  vertebrate  series. 

III.  Phylogeny  of  the  types  of  vertebrate  ileo-colic  junction 
and  caecum,  and  their  probable  lines  of  evolution. 

IV.  Detailed  morphology  of  the  human  csecum  and  vermiform 
appendix. 

I.   GENERAL  REVIEW  OF  THE  MORPHOLOGY  AND  PHYSI- 
OLOGY OF  THE  VERTEBRATE  INTESTINE. 

We  have  seen  that  the  intestinal  tube  of  all  vertebrates  is  the 
product  of  two  of  the  embryonal  blastodermic  layers,  the  entoderm 
and  mesoderm.  The  former  furnishes  the  characteristic  and  car- 
dinal elements  of  the  digestive  tract,  viz.,  the  secretory  and  absorb- 
ing epithelium  of  the  mucous  membrane  and  of  the  accessory 
digestive  glands,  the  liver  and  pancreas. 

From  the  mesoderm,  on  the  other  hand,  are  derived  the  mus- 
cular and  connective  tissue  coats  which  surround  the  epithelial 
tube  and  contribute  to  the  thickness  of  the  intestinal  wall,  as  well 
as  the  blood  vessels  and  lymphatics.  The  alimentary  canal  sepa- 
rates from  the  yolk-sac  of  the  embryo  by  the  development  of 
cranial,  caudal  and  lateral  folds,  and  at  an  early  period  communi- 
cates with  the  neural  canal  by  the  primitive  postanal  gut  (cf  p. 
23).  This  connection  subsequently  becomes  lost.  The  oral  and 
anal  openings,  by  means  of  which  the  alimentary  canal  communi- 


MORPHOLOGY  AND  PHYSIOLOGY  OF  VERTEBRATE  INTESTINE.     191 

cates  with  the  exterior,  are  formed  secondarily  by  entodermal 
invaginations  which  finally  break  through  into  the  lumen  of  thjB 
canal  (cf  p.  24).  

At  an  early  embryonic  stage  the  alimentary  canal  appears 
therefore  as  a  straight  cylindrical  tube  running  cephalo-caudad 
in  the  long  axis  of  the  body-cavity,  and  suspended  by  the 
primitive  mesentery  from  the  ventral  aspect  of  the  chorda 
dorsaHs. 

In  Amphioxus,  the  cyclostomata,  certain  teleosts,  dipnceans  and 
lower  amphibians  the  canal  remains  permanently  in  this  condi- 
tion (cf.  Fig.  310). 

In  the  remaining  vertebrates  the  uniform  non-differentiated 
tube  of  the  embryo  develops  further  and  appears  more  or  less 
distinctly  divided  into  a  proximal  segment,  WiQforegut,  a  central 
segment,  the  midgut,  and  a  distal  segment,  the  hindgut,  or  endgui. 
This  differentiation  of  the  tube  into  successive  segments  is  closely 
connected  with  the  character  and  quantity  of  the  food  habitu- 
ally taken  and  with  the  method  and  rapidity  of  its  elaboration 
in  the  process  of  digestion,  absorption  and  excretion.  In  general 
the  foregut  is  formed  by  the  segment  which  succeeds  to  the  oral 
cavity,  and  includes  the  pharynx,  oesophagus  and  stomach.  The 
midgut  is  composed  of  a  longer  or  shorter  narrower  tube  of  nearly 
uniform  caliber,  the  small  intestine,  which  follows  the  gastric  dila- 
tation. Even  in  forms  in  which  the  stomach  is  not  distinctly 
differentiated  (cf  p.  40)  the  connection  of  the  biliary  duct  with 
the  intestinal  canal  serves  to  separate  the  fore-  and  midgut.  The 
hindgut  or  large  intestine  is  usually  separated  from  the  preceding 
segment  by  an  external  circular  constriction,  with  a  correspond- 
ing annular  valve  or  fold  of  the  mucous  membrane  in  the 
interior. 

The  beginning  of  the  large  intestine  is  marked  in  many  forms 
by  the  development  of  an  accessory  pouch  or  diverticulum,  the 
caecum.  The  hindgut  extends  from  its  junction  with  the  midgut 
to  the  cloacal  or  anal  opening. 


192  LARGE  AND  SMALL  INTESTINE. 

1.  Midgut  or  Small  Intestine. 
•  The  small  intestine  is  the  segment  of  the  alimentary  canal  in 
which  digestion  of  the  non-nitrogenous  food  substances  takes 
place,  and  which  affords  the  necessary  area  of  mucous  surface  for 
the  absorption  of  all  digested  matters.  Consequently  the  char- 
acter and  habitual  quantity  of  the  food  here  elaborated  exerts  a 
very  marked  influence  on  the  length  of  the  small  intestine,  i.e.,  on 
the  extent  of  the  digestive  and  absorbing  surface  represented  by 
its  mucous  membrane. 

The  relative  length  of  the  small  intestine  in  any  individual 
form  will  vary  with  both  the  quantity  and  volume  of  the  food 
and  with  the  rapidity  of  the  metabolic  processes.  Animals,  in 
which  digestion  is  rapid  and  the  usual  food  small  in  bulk  and 
concentrated  in  its  nutrient  qualities,  have  a  relatively  short 
intestine,  while  the  canal  is  longer  in  forms  subsisting  on  food 
which  is  bulky  and  which  demands  considerable  time  for  its 
elaboration.  Hence  we  find  the  relatively  shortest  intestine  in 
carnivora,  the  longest  in  herbivora,  while  the  canal  in  omnivora 
occupies  an  intermediate  position  in  regard  to  its  relative  length. 

The  rapidity  of  tissue-metabolism  also  exerts  a  marked  influ- 
ence on  the  length  and  development  of  this  portion  of  the  alimen- 
tary canal. 

In  the  warm-blooded  animals  (mammals  and  birds)  the  tissue- 
changes  are  constant  and  rapid  and  call  for  a  large  amount  of 
nutrition  within  a  given  period,  while  the  metabolic  processes  in 
the  cold-blooded  vertebrates  (reptiles,  amphibia  and  fishes)  are 
slow,  these  animals  being  able  to  go  without  food  for  long  periods. 
Consequently  in  the  former  class  the  small  intestine  is  relatively 
much  longer  than  in  the  latter.  Thus  in  certain  birds  and  her- 
bivorous mammals  the  small  intestine  exceeds  the  total  length  of 
the  body  many  times.  This  influence  of  the  quantity  and  quality 
of  the  food  on  the  length  of  the  intestinal  canal  is  seen,  for  ex- 
ample, very  well  during  the  course  of  development  in  the  frog. 

The  increase  in  the  length  of  the  intestine,  and  the  consequent 
varying  degrees  of  coiling  and  convolution,  are  therefore  second- 


PLATE    CLIII. 


Fig.  303. — Mucous  surface  of  small 
intestine  of  a  species  of  African  antelope, 
Cervicapra  arundinacea.  (Columbia  Uni- 
versity Museum,  No.  1843.) 


Fig.  304. — Mucous  surface  of  small 
intestine  of  Phocsena  commums,  porpoise. 
(Columbia  University  Museum,  No.  1057.) 


PLATE   CLIV. 


Fig.  305. — Mucous  membrane  of  mid-gut  of  LopMus  piscatorius,  the  angler,  18  cm. 
caudad  of  pylorus.     (Columbia  University  Museum,  No.  1838.) 


Figs.  306,  307. — Intestinal  mucous  membrane  of  logger-head  turtle,   ThaJassochelys  caretta. 
(Columbia  University  Museum,  No.  1839.) 
Fig.  306.— Mid-gut. 
Fig.  307.— End-gut. 


PLATE   CLV. 


Fig.  :W8.— Adult  human  subject.  Mucous  membrane  of 
pyloro-duodenal  junction  and  of  duodenum.  (Columbia  Uni- 
versity Museum,  No.  1840.) 


PLATE    CLVr. 


PeRICARD'.UM 


GASTRIC 

oilatat;on 


INTESTINAL 
CANAL  WITH 
SPIRAL  FOLD 
OF    MUCOSA 


Fig.  309.— Adult  liumaii  subject.  Mucous 
membrane  of  small  intestine,  showing  arrangement 
of  valvulse  conniventes  in  successive  portions  of 
jejunum  and  ileum.  (Columbia  University  Mu- 
seum, No.  1841.) 


Fig.  310. — Peiromyzon  marinus,  lam- 
prey. Entire  alimentary  canal  below 
pericardium.  (Columbia  University  Mu- 
seum, No.  1575.) 


PLATE    CLVII. 


STOMACH 


PYLORIC 
OECUM 


ILEO-COLIC 
JUNCTION 


Fig.  311. — Echelus  coin/er,  Conger  eel.     Alimentary  canal,  stomach,  mid-  and  bind- 
gut,  liver,  and  spleen.     (Columbia  University  Museum,  No.  1430.) 


END-GUT 


MID-GUT 


ILEO-COLIC 
VALVE 


Fig.  312. — Echelus  conger,  Conger  eel.    Ileo-colic  junction,  opened. 
(Columbia  University  Museum,  No.  1434.) 


PLATE    CLVIII. 


ILEO-COLIC 
VALVE 


END-GUT 


Fig.  313. — Echelus  coiujer.  Conger  eel.  Section  of  mid-  and  end-gut, 
with  ileo-colic  junction,  hardened.  (Columbia  University  Museum,  No. 
1349.) 


ILEO-COLIC  JUNC- 
TION    WITH     PROBE 
PASSED  THROUGH 
CONSTRICTED   ILEO- 
COLIC VALVE   OPEN- 
ING 


NIID-GUT 
OPENED 


ILEO-COLIC 
VALVE 


END-GUT         I'lG-     Z\T^.—Pleuronectes    maculatns, 
OPENED     flounder.     Ileo-colou,   opened  to   show 

ileo-colic  valve.    (Columbia  University 

Museum,  No.  1493.) 


Fig.  314. — Gadus  callarias,  cod-fish.  Ileo-colic  junction.  Intes- 
tine on  each  side  opened,  with  probe  passed  through  constricted 
opening  of  ileo-colic  valve.    (Columbia  University  Museum,  No.  1260.) 


PLATE    CLIX. 


RECTAL   GLAND 


BENT  PROBE 
PASSED  INTO 
I  NTE  ST  INALl 
OPENING  OF 
RECTAL  GLAND 


ORE-GUT    DIV:DEa 


VAS    DEFERENS 


END-GUT  WITH    SPIRAL 
MUCOUS    FOLD 


ROD  PASSED         INTO 

CLOACAL  OPENING  OF 
ALIMENTARY    CANAL 

PROBE  PASSED  INTO 
OPENING  OF  GENITO- 
URINARY    PAPILLA 

PROBE    IN    ABDOM- 
INAL   PORE 


in  i^^u'-  -^l^-T '^^'"'^"■^  <L«"*«'  dog-shark.  ^.     Genito-urinary  tract  and  cloaca  m  situ. 
(Columbia  Lniversity  Museum,  Xo.  1694.) 


PLATE    CLX. 


PYLORIC 
APPENDICES 


ILEO-COLIC 
JUNCTION 


—    —    -    SPLEEN 


Fig.  317. — Acdpenser  sturio,  sturgeon.    Alimentary  canal.     (Columbia  Uni- 
versity Museum,  Nos.  1826,  1827,  and  1828.) 


MIDGUT  OR  SMALL  INTESTINE.  193 

ary  acquired  characters,  depending  for  their  development  upon 
the  habitual  kind  and  volume  of  the  food.  Additional  provisions 
for  increasing  the  efficiency  of  the  digestive  apparatus  are  en- 
countered throughout  the  whole  of  the  intestinal  canal.  In  many 
forms  the  digestive  secretory  and  absorbing  area  is  augmented 
by  the  development  of  folds,  valves,  diverticula,  villi  and  papillae 
from  the  mucous  surface  of  the  intestine.  Certain  valves  and 
folds,  moreover,  both  control  the  direction  in  which  the  contents 
of  the  canal  move  and  retain  the  same  for  a  longer  period  in  the 
intestinal  segment  in  which  they  develop.  Such  folds  appear 
especially  well  developed  in  the  intestine  of  certain  cyclostomes, 
selachians  and  dipnceans  (cf  Figs.  203  and  204).  In  these  forms 
the  alimentary  canal  is  usually  short  and  straight,  and  the  fold 
which  has  a  typical  spiral  course  and  projects  far  into  the  lumen 
of  the  gut,  evidently  makes  up  to  a  very  large  extent  for  the 
shortness  of  the  intestine,  serving  the  threefold  purpose  of 

(a)  Increasing  the  digestive  and  absorbing  surface ; 

(6)  Prolonging  the  period  of  retention  of  the  food-substances  in 
the  intestine,  and  thus  increasing  the  time  available  for  elabora- 
tion and  absorption. 

(c)  Regulating  the  direction  in  which  the  intestinal  contents 
move. 

We  will  see  presently  that  a  similar  spiral  mucous  fold  is  also 
encountered  in  some  of  the  higher  vertebrates,  especially  in  the 
large  intestine.  Examples  are  found  in  the  well-developed  spiral 
valve  in  the  caeca  of  the  ostrich  (Fig.  341),  the  similar  fold  in 
the  large  intestine  of  many  rodents  (Figs.  387  and  388)  and  in  the 
crescentic  plicae  of  the  primate  large  intestine  (Figs.  471,  472  and 
473). 

To  the  same  physiological  category  belong  the  digestive  diver- 
ticula of  the  intestinal  canal,  such  as  the  pyloric  appendices  of  the 
midgut  found  in  many  teleosts  and  ganoids  (cf  p.  119)  and  the 
varieties  of  caeca  or  blind  diverticula  of  the  hindgut  encountered 
throughout  the  vertebrate  series.  They  all  function  as  reservoirs 
which  increase  the  available  digestive  and  absorbing  surface  and 

13 


194  LARGE  AND  SMALL  INTESTINE. 

which  in  addition  are  especially  adapted  to  retain  substances 
difficult  of  digestion  until  the  processes  of  elaboration  have  been 
completed. 

Divisions  of  the  Small  Intestine. — In  the  higher  forms  the  segment 
of  the  small  intestine  which  succeeds  to  the  pylorus  is  distin- 
guished as  the  duodenum.  Into  it  empty  the  ducts  of  the  liver 
and  pancreas.  In  some  animals  a  pear-shaped  enlargement  is 
found,  corresponding  to  the  duodenal  antrum  of  the  human  intes- 
tine, as  the  dilated  proximal  portion  of  the  duodenum  immedi- 
ately beyond  the  pylorus  is  called.  Examples  of  this  condition 
are  furnished  by  the  cetaceans,  several  rodents,  the  llama  and 
dromedary  and  the  koala  (Phascolarctos). 

In  the  birds  and  in  many  mammals  (e.  g.,  dog,  Fig.  200,  and 
many  rodents,  as  the  rabbit)  the  duodenum  is  drawn  out  into  a 
long  loop  surrounding  the  pancreas. 

Structure  of  the  Small  Intestine.  1.  Secretory  Apparatus. — The 
glands  whose  ducts  empty  into  the  small  intestine  and  which 
furnish  the  digestive  secretions,  may  be  divided  as  follows : 

(a)  Glands  situated  in  the  substance  of  the  intestinal  walla. 

Two  kinds  are  distinguished : 

1.  Brunner's  glands,  small  acinous  glands  confined  to  the  first 
part  of  the  duodenum. 

2.  Glands  of  Lieberkiihn,  small  csecal  pits  distributed  not  only 
over  the  entire  small  intestine,  but  also  found  in  the  mucous 
membrane  of  the  large  intestine. 

These  structures  furnish  the  intestinal  juice,  whose  chief  func- 
tion is  the  conversion  of  starches  into  sugar,  while  aiding  in 
carnivorous  animals  also  the  digestion  of  proteid  substances. 
The  glands  are  hence  best  developed  in  herbivora,  while  in 
carnivora  they  are  present  in  diminished  numbers  since  they 
assist  in  the  digestion  of  proteid  substances. 

The  size  and  number  of  these  glands  also  depends  on  the 
amount  of  food  digested  within  a  given  period.  When  a  con- 
siderable quantity  of  digestive  fluid  is  required,  in  order  to  obtain 
the  nutritive  value  of  the  food  for  the  organism  rapidly,  the 


ABSORBING  APPARATUS  OF  SMALL  INTESTINE.  195 

glandular  apparatus  of  the  intestine  will  be  well  developed. 
Hence  mammalia,  in  whom  these  conditions  exist,  possess  both 
the  glands  of  Brunner  and  of  Lieberkiihn.  In  birds  the  latter 
structures  are  still  found,  but  the  former  are  absent,  while  amphi- 
bia and  fishes  are  devoid  of  both  kinds.  In  these  lower  verte- 
brates the  typical  intestinal  glandular  apparatus  of  the  higher 
forms  is  to  a  certain  extent  replaced  by  small  pits  and  depres- 
sions of  the  mucous  membrane  bounded  by  reticular  folds. 

(6)  Glands  situated  outside  the  intestinal  tube,  into  whose  lumen 
their  ducts  empty. 

The  liver  and  pancreas  fall  under  this  head.  The  liver  func- 
tions in  the  digestion  of  the  fatty  substances  of  the  food,  while 
the  secretion  of  the  pancreas  converts  the  starches  into  sugars, 
and  aids  in  the  digestion  of  albumenoid  substances  and  to  a 
lesser  degree  in  that  of  the  fats. 

2.  Absorbing  Apparatus  of  Small  Intestine. — The  mucous  membrane 
of  the  intestine  is  provided  with  villi,  containing  lymphatics,  by 
whose  agency  the  digested  matters  are  absorbed.  These  struc- 
tures are  developed  in  individual  forms  in  direct  proportion  to 
the  ease  and  rapidity  with  which  the  food  is  habitually  absorbed. 

The  more  rapid  and  complete  the  digestion  is  the  greater  will  be 
the  amount  of  digested  nutritive  material  at  any  given  time  in  the 
intestine,  and  the  greater  will  be  the  development  of  the  absorb- 
ing structures.  Hence  the  villi  of  the  small  intestine  are  espe- 
cially large  and  prominent  in  the  carnivora,  while  they  are  small 
and  insignificant  in  herbivora  and  omnivora.  Intestinal  villi  are 
found  in  nearly  all  mammals  and  in  many  birds.  Fig.  300  shows 
the  villi  of  the  intestinal  mucous  membrane  in  a  carnivore  mam- 
mal {Ursus  maritimus,  polar  bear)  and  Fig.  301  the  same  struc- 
tures in  the  cassowary  ( Casuarius  casuarius)  in  which  bird  they 
are  very  well  developed.  The  villi  are  not  confined  to  the  two 
highest  vertebrate  classes,  but  are  encountered  also  in  the  mucous 
membrane  of  the  midgut  in  certain  reptiles,  notably  the  ophidia. 

Fig.  302  shows  the  intestine  mucous  membrane  of  the  boa  con- 
strictor with  well-developed  and  prominent  villous  projections. 


196  LARGE  AND  SMALL  INTESTINE. 

Some  birds,  such  as  the  snipes,  herons  and  crows,  have  in  place 
of  the  intestinal  villi  projecting  folds  of  the  mucosa,  often  arranged 
in  a  reticular  manner.  This  type  is  prevalent  in  amphibia  and 
fish  (Fig.  112,  distal  segment  of  midgut).  Collections  of  lymphoid 
tissue  in  the  mucous  membrane  of  the  small  intestine,  either 
aggregated  to  form  Peyer's  patches  (Fig.  309)  or  as  solitary  fol- 
licles, are  only  found  in  the  two  highest  vertebrate  classes,  birds 
and  mammals.  In  the  former  they, appear  scattered  over  the 
surface  of  the  mucous  membrane,  in  the  latter  they  may  be 
arranged  in  aggregations  or  regular  rows.  They  are  not  secreting 
structures,  but  their  exact  function  in  absorption  is  not  known. 
This  lymphoid  or  adenoid  tissue  in  certain  forms  is  especially 
well  developed  at  the  ileo-colic  junction,  forming  the  lymphatic 
sac  of  some  rodents,  as  lepus  (cf.  Fig.  386).  It  is  not  confined  to 
the  small  intestine,  but  is  found  in  the  large  intestine  as  well. 
At  times  it  appears  especially  well  developed  in  the  terminal  por- 
tion of  the  csecal  pouch  (appendix),  as  in  Lepus  (Fig.  388). 

The  valvulm  conniventes  or  valves  ofKerkring  of  the  human  small 
intestine  serve  to  very  greatly  increase  the  secreting  and  absorb- 
ing mucous  surface.  They  are  not  found  in  this  complete  devel- 
opment in  any  other  mammals,  although  a  very  few  forms  pre- 
sent a  transverse  reduplication  of  the  intestinal  mucosa  and  the 
circular  layer  of  muscular  fibers.  An  example  of  this  is  found  in 
the  intestinal  mucous  membrane  of  a  species  of  antelope,  shown 
in  Fig.  303. 

The  complete  development  of  the  valvulse  conniventes  in  man 
is  possibly  also  associated  with  a  mechanical  function  in  connec- 
tion with  the  upright  posture.  In  some  mammalia,  as  in  certain 
rodents  and  the  porpoise  (Fig.  304),  the  mucous  membrane  of  the 
terminal  part  of  the  small  intestine  is  thrown  into  longitudinal  folds. 

The  mucosa  of  the  midgut  in  the  lower  vertebrates  may  be 
smooth,  or  thrown  into  longitudinal  folds,  or  the  longitudinal 
folds  may  become  connected  by  oblique  and  transverse  secondary 
folds,  resulting  finally  in  a  more  or  less  complicated  reticulated 
pattern  of  crypts.     A  very  good  example  of  the  type-form  from 


ABSOBBINQ  APPABATUS  OF  SMALL  INTESTINE.  197 

which  the  more  complicated  conditions  are  derived  is  seen  in 
Fig.  305,  showing  the  mucous  membrane  of  the  midgut  in  Lophius 
piscatorius,  the  angler.  The  specimen  is  taken  18  cm.  from  the 
pylorus  and  shows  a  ground  plan  of  longitudinal  plicae  connected 
by  short  oblique  cross  folds. 

Fig.  306,  showing  the  midgut  mucosa  of  the  loggerhead  turtle 
{Thalassochelys  caretta),  exhibits  the  same  arrangement  further 
developed,  resulting  in  a  fine  reticulated  pattern,  while  in  the 
endgut  of  the  same  animal  the  primitive  longitudinal  folding  is 
resumed  (Fig.  307). 

The  number  and  size  of  the  human  valvulse  conniventes  vary 
in  different  parts  of  the  small  intestine  (Fig.  309).  They  are  not 
usually  found  in  the  beginning  of  the  duodenum  (Fig.  308),  but 
commence  in  the  second  or  descending  portion. 

They  become  very  large  and  closely  packed  immediately  be- 
yond the  common  entrance  of  the  biliary  and  pancreatic  ducts 
and  continue  to  be  well  developed  and  numerous  throughout  the 
rest  of  the  duodenum  and  upper  half  of  the  jejunum  (Figs.  308 
and  309).  From  here  on  they  become  smaller,  more  irregular 
and  less  closely  packed,  and  finally  in  the  terminal  two  feet  of  the 
ileum  disappear  almost  entirely  (Fig.  309).  This  varying  develop- 
ment of  the  valvules  is  the  chief  reason  why  a  given  segment  of 
the  ileum  weighs  less  than  a  corresponding  length  of  the  jejunum. 
This  reduction  in  the  fold-formation  of  the  intestinal  mucosa 
toward  the  terminal  portion  of  the  midgut  is  seen  even  in  the 
lower  vertebrates.  Thus  in  Fig.  112,  showing  the  entire  intesti- 
nal tract  of  the  conger  eel,  Echelus  conger,  in  section,  the  plicae 
of  the  mucous  membrane  in  the  proximal  segment  of  the  midgut, 
at  and  immediately  beyond  the  entrance  of  the  biliary  duct,  are 
prominent  and  numerous.  This  redundancy  continues  but 
slightly  reduced  in  the  descending  limb  of  the  intestinal  loop, 
while  in  the  ascending  limb  and  up  to  the  ileo-colic  junction  the 
folds  are  reduced  to  a  fine  reticulated  meshwork.  Beyond  the 
ileo-colic  valve  plate,  in  the  short  endgut,  the  mucosa  again  pre- 
sents numerous  pointed  reduplications. 


198  LARGE  AND  SMALL  INTESTINE. 

II.  ENDGUT  OR  LARGE  INTESTINE. 

In  this  segment  of  the  intestinal  canal  the  undigested  remnants 
of  the  food  are  collected  and  evacuated  from  time  to  time. 

In  addition,  the  mucous  membrane  of  the  large  intestine  ab- 
sorbs all  digested  material  which  is  passed  from  the  small  intes- 
tine. While  digestion  of  food-substances  will  not  be  inaugurated 
in  the  large  intestine,  material  already  in  the  process  of  digestion 
and  mixed  with  the  intestinal  juices  of  the  preceding  segment, 
will  be  further  elaborated  in  this  portion  of  the  canal  and  the 
nutritive  products  absorbed.  This  is  especially  the  case  in  her- 
bivora  and  omnivora,  whose  food  is  bulky,  containing  a  large 
amount  of  refuse  material,  and  is  hence  only  slowly  digested. 
On  the  other  hand  the  food  of  the  carnivora  is  easily  and  rapidly 
digested  and  absorbed.  After  passing  through  the  small  intestine 
hardly  any  substances  remain  which  are  capable  of  digestion  and 
absorption.  Hence  the  large  intestine  of  herbivora  and  omnivora 
is  uniformly  longer  in  proportion  to  the  small  intestine  than  it  is 
in  carnivorous  animals.  In  the  former  this  segment  of  the  canal 
functions  as  an  accessory  digestive  apparatus  and  hence,  as  we 
will  see,  often  develops  accessory  structural  modifications,  such  as 
a  large  caecum  and  spiral  colon,  while  in  the  latter  it  acts  almost 
solely  as  a  canal  for  the  evacuation  of  the  indigestible  remnants. 

Again,  the  large  intestine  is  better  developed  in  the  higher 
animals,  in  mammalia  and  to  a  lesser  degree  in  birds,  in  whom 
the  functional  demands  for  nutrition  are  active  and  require  that 
a  relatively  large  amount  of  food  should  pass  through  the  diges- 
tive tract  in  a  given  time.  On  the  other  hand  in  the  lower 
cold-blooded  vertebrates  the  metabolism  is  less  active,  less  food  is 
taken  and  it  is  not  necessary  to  secure  all  the  nutrient  material 
contained  in  the  same  for  the  organism.  The  great  differences 
observed  in  the  vertebrate  series  in  regard  to  length,  width 
and  structure  of  the  large  intestine  depend  upon  these  physio- 
logical conditions.  The  divisions  of  the  human  large  intestine 
into   caecum,  ascending,  transverse  and   descending  colon,   sig- 


ENDQUT  OR  LARGE  INTESTINE.  199 

moid  flexure  and  rectum  are  found  only  in  the  primates,  and 
here  not  uniformly. 

In  the  lower  vertebrate  classes  the  endgut  is  very  short,  corre- 
sponding only  to  the  pelvic  segment  of  the  Mammalia  (rectum), 
a  colon  proper  being  absent  in  these  forms  (cf  Fig.  112,  Echelus 
conger).  The  human  large  intestine  exhibits  a  very  character- 
istic structure.  Throughout  the  greater  part  of  the  colon  the 
longitudinal  muscular  layer  is  mainly  disposed  in  the  form  of 
three  bands  or  taenia  (ligamenta  coli).  The  canal  itself  is  longer 
than  these  bands,  thus  producing  a  folding  of  the  walls  in 
the  form  of  three  rows  of  pouches  (cellulse  coli),  in  the  intervals 
between  the  bands.  The  pouches  of  each  row  are  separated  from 
each  other  externally  by  constrictions,  internally  by  projecting 
crescentic  folds  (plicae  coli)  (Figs.  4.71,  472  and  474). 

This  arrangement  of  the  large  intestine  is  also  found  in  the 
monkeys  (Fig.  473)  and  in  certain  Rodents  (Fig.  474). 

In  other  mammals  the  large  intestine  is  smooth  and  cylindri- 
cal and  the  longitudinal  layer  of  muscular  fibers  uniform  (Fig. 
475). 

In  general  the  vertebrate  large  intestine  is  wider  than  the  small, 
usually  in  the  proportion  of  5  : 1  or  6  : 1. 

In  some  ruminant  Herbivora,  however,  the  great  length  of  the 
colon  leads  to  a  reduction  of  the  caliber  in  certain  segments  so 
that  the  large  intestine  does  not  exceed  the  width  of  the  small, 
or  even  falls  below  the  same. 

The  length  of  the  large  intestine,  as  in  man,  is  usually  much 
less  than  that  of  the  small  intestine.  As  already  stated  this 
disproportion  is  more  marked  in  Carnivora  than  in  Herbivora. 

The  ratio  in  length  of  the  large  to  the  small  intestine  is  very 
low  in  the  Seals  (1:14),  and  in  several  Edentates,  as  Myrmecophaga, 
Tamandua  and  Bradypus  (1:9-11). 

In  the  carnivorous  mammals  it  ranges  1 : 5-7. 

In  some  of  the  ruminant  Herbivora,  as  the  cow  and  sheep,  it  is 
1:4,  while  in  the  deer,  horse,  certain  Rodents  (as  Lepus  and  Crice- 
tus)  it  reaches  as  high  as  1 : 2  or  1:3. 


200  ILEO-COLIC  JUNCTION. 

The  large  intestine  is  usually  relatively  short  in  birds,  reptiles, 
amphibia  and  fish. 

In  the  Cassowary  the  length  of  the  large  to  the  small  intestine 
is  1:6. 

In  some  of  the  birds  of  prey  (eagle)  the  proportion  falls  as  low 
as  1:68  or  70. 

Exceptions  to  the  general  rule  are  furnished  by  some  of  the 
herbivorous  Cetaceans  and  by  the  Dugong  (Halicore)  in  whom 
the  large  intestine  is  twice  as  long  as  the  small.  Again  in  the 
Ostrich  the  large  intestine  in  one  example  measured  40',  while 
the  length  of  the  small  intestine  was  only  22'.  This  unusual 
development  of  the  large  intestine  indicates  the  necessity  of 
retaining  the  food,  which  is  bulky  and  difficult  of  digestion,  until 
the  elaboration  is  completed.  The  same  significance  belongs  to 
the  enormously  developed  cseca  of  these  birds  (cf  p.  204). 

The  separation  of  the  small  and  large  intestine  is  marked 
externally  by  the  cxcum,  when  present,  and  internally  by  the 
valve  of  the  colon.  The  details  of  the  vertebrate  ileo-colic  junc- 
tion will  be  considered  in  the  following  pages. 

II.   SERIAL  REVIEW  OF  THE  ILEOCOLIC  JUNCTION  AND  CON- 
NECTED STRUCTURES  IN  VERTEBRATES. 

I.  FISHES. 

In  the  Cyclostomata  there  is  no  differentiation  between  the 
mid-  and  hindgut.  Fig.  310  shows  the  entire  alimentary  canal  of 
Petromyzon  marinus,  the  lamprey,  caudad  of  the  pericardium. 

In  some  fishes  the  midgut  is  differentiated  from  the  hindgut 
by  an  external  circular  constriction,  corresponding  to  an  annular 
projecting  fold  of  the  mucosa  in  the  interior  which  resembles  the 
pyloro-duodenal  valve.  There  is  no  caecum,  and  the  short  hind- 
gut empties  into  the  cephalic  and  ventral  aspect  of  the  cloaca. 
Fig.  311  shows  the  entire  intestinal  tract  of  a  Teleost  fish,  Echelus 
conger,  the  conger  eel.  The  midgut,  provided  at  the  beginning 
with  a  short  globular  pyloric  appendix  (cf  p.  119),  constitutes  the 
longest  individual  segment  of  the  canal.    The  hindgut,  separated 


PLATE   CLXI. 


LEO-COLIC 
JUNCTION 


->  OESOPHAGUS 


STOMACH 


PANCREAS 


_  DUODENUM 


Fig.  318. — Rana  cateshiuna,  bull-frog.      Alimentary  canal  and  appen- 
dages.    (Columbia  University  Museum,  No.  1454.) 


PVLORODUODENAL 
JUNCTION 


LIVER 


PANCREAS 


_^  I  LEO-COLIC 
JUNCTION 


Fig.  320. — C'ryptobranchus 
alleghaniensis,  hellbender.  Ileo- 
colic junction.  (Columbia  Uni- 
versity Museum,  No.  1711.) 


Fig.  319. — Necturus  maculatus,  mud-puppy.  Ali- 
mentary canal  and  appendages.  (Columbia  Univer- 
sity Museum,  No.  1582.) 


PLATE    CLXII. 


Fig.    3"21. — Alligator  mississippiensis,  alligator.      Ileo-colou ;    dried 
preparation.     (Columbia  University  Museum,  No.  179.) 


MID-GUT 


ILEO-COLIC 
JUNCTION 
WITH   VALVE 
CONSTRICTION 


Fig.  322. — Helodenna  fmspednm,  Gila  monster. 
bia  University  Museum,  No.  xf  §5.) 


(Colum- 


PLATE    CLXIII. 


Fig.  323. — Pseudemys  elegans,   poud-turtle. 
Museum,  No.  1069.) 


(Columbia  University 


probe  passed 
|through  ileo- 
colic CONSTRIC- 
jTION 

—  -OECUM 


Fig.  324. — Pseudemys  elegans,  pond-turtle.  Ileo-colic  junction,  opened. 
(Columbia  University  Museum,  No.  1524.) 


PLATE    CLXIV. 


BEGINNING    OF 
MID-GUT 
DUODENO-COLIC 
ISTHMUS 


PANCREAS 


ILEO-COLIC 
JUNCTION 


MID-GUT  FORM- 
ING APEX  OF 
I  N  TE  ST  I  N  AL 
LOOP 


Fig.  325. — Chelydra  serpentaria,  snapping-turtle.  Intestinal 
canal,  pancreas,  and  spleen.  (Columbia  University  Museum, 
No.  1369.) 


Fig.  326. — Iguana  tnhcrcHhita,  iguana.     1  Ico-coiic  junction  and  Oit'cum  ; 
dried   preparation.     (Columbia  University  Museum,  No.  243.) 


PLATE    CLXV. 


TRANSITION  BEND 
FROM  OECAL  POUCH 
TO  END-GUT  PROPER 


ILEO-COLIC 
JUNCTION 


Fra.  327. — Ljnana  inherculata,  iguana.  Mid-gut,  ileo-colic  junction, 
csecum,  and  end-gut ;  dried  preparation.  (Columbia  University  Museum, 
No.  178.) 


PROXIMAL     COM- 
PARTMENT     OF 
C/ECAL       POUCH 
SEPARATED   FROM 
REMAINDER    BY 
CIRCULAR  VALVU- 
LAR   FOLD  WITH 
CENTRAL  OPENING 


ILEO-COLIC  OPENING 
IN  ANNULAR  SPHINC- 
TER   VALVE 


TRANSITION      OF 
C>eCAL      POUCH 
INTO      END-GUT 
PROPER 


Fig.  328. — Inuana  tnbercnlata,  iguana.     Ileo-colic  junction    and  caecum 
in  section.     (Columbia  University  Museum,  No.  1321.) 


PLATE   CLXVI. 


ILEO-COLIC 
VALVE 


CIRCULAR  VALVULAR 

FOLD  WITH   CENTRAL 

OPENING 


CRESCENTIC   VALVES 
OF  C/ECAL   POUCH 


TRANSITION    BEND 
FROM  CjECAL  pouch 
TO   END-GUT    PROPER 


Fig.  329. — Drawing  taken  from  same  pro2)aratiou  (No.  1321J  to  elucidate  more  clearly 
internal  structure  of  csecal  pouch. 


ANNULAR  SPHINC- 
TER VALVE  AT  ILEO- 
COLIC JUNCTION 


CIRCULAR  VALVULAR 
FOLD  WITH  CENTRAL 
OPENING      SEPARAT- 
ING    PROXIMAL 
C/CCAL   COMPART- 
MENT    FROM      RE- 
MAINDER OF  POUCH 


TRANSITION  OF 
OECAL  POUCH 
INTO  END  GUT 
PROPER 


Fig.  330. — C.i/d?«ra /ei-M,  smooth-backed  cyclura.     Ileo-colic  junction  and  ca?cum 
in  section.     (Columbia  University  Museum,  No.  1523.) 


PLATE   CLXVII. 


END-GUT     OPENED 

SHOWING    SPIRAL 

VALVE  PROJECTION 

OF    MUCOSA 


LEO-COLIC 
JUNCTION 


J  IL?0-COLIC 
I  JUNCTION 


Fig.  331. — Eanectes  mariuiis,  anaconda.  Mid-  and 
end-gut,  with  ileo-colic  junction  and  csecum.  (Co- 
lumbia University  Museum,  No.  1JI5.) 


■valve  folds  in 
'distal  part  of 

END-GUT 


Fig.  '3'32.—Eunectes  marhms,  anaconda. 
Mid-  and  end-gut,  with  ileo-colic  junction  and 
caecum  laid  open.  (Columbia  University  Mu- 
seum, No.  17uy.) 


9^ 


f^5 


AMPHIBIAN  AND  REPTILIAN  TYPES.  201 

from  the  preceding  by  a  constriction,  is  very  short  and  of  large 
caliber.  Fig.  312  shows  the  broad  annular  valve  with  central  cir- 
cular opening  which  separates  mid-  and  hindgut  in  the  interior, 
and  Fig.  313  the  ileo-colic  junction  in  section  in  the  same  animal. 
A  similar  type  of  ileo-colic  junction  is  seen  in  other  Teleosts,  as 
in  Gadiis  callarias,  the  cod  (Fig.  314),  Pleuronectes  maculatus,  the 
flounder  (Fig.  315),  and  in  some  Ganoids,  as  Acdpenser  sturio,  the 
sturgeon  (Fig.  212).  .  In  some  Selachians  an  appendicular  diver- 
ticulum, the  so-called  "  rectal "  or  "  digitiform  gland,"  is  found 
connected  with  the  terminal  segment  of  the  gut  near  the  entrance 
of  the  same  into  the  cloaca  (Fig.  316). 

n.  AMPHIBIA. 

The  ahmentary  canal  is  simple  and  usually  comparatively  short. 
There  is  no  csecal  pouch.  Differentiation  of  mid-  and  endgut  is 
usually  marked  externally  by  a  constriction  and  by  the  increased 
caliber  of  the  terminal  intestinal  segment. 

Fig.  318  shows  the  alimentary  canal  of  the  bull-frog,  Rana 
cateshiana,  Fig.  319  that  of  a  Urodele  Amphibian,  Necturus  maaa- 
latus,  and  Fig.  320  the  ileo-colic  junction  isolated  in  Grypto- 
branchus  alleghaniensis,  the  hellbender. 

m.  REPTILIA. 
In  reptiles  a  well-marked  differentiation  of  small  and   large 
intestine  is  the  rule. 

Four  types  of  ileo-colic  junction  are  encountered  in  this  class : 

1.  The  transition  from  small  to  large  intestine  is  marked  by  the 
greatly  increased  caliber  of  the  latter  and  by  an  annular  valve 
in  the  interior.  An  example  of  this  type  is  furnished  by  Alliga- 
tor mississippiensis  (Fig.  321)  and  a  similar  form  is  encountered  in 
some  lizards,  as  Heloderma  suspectum,  the  Gila  monster  (Fig.  322). 

2.  The  large  intestine  immediately  beyond  the  ileo-colic  junc- 
tion protrudes  along  the  convex  border  to  form  a  rudimentary 
lateral  csecum.  This  type  is  found  in  many  Chelonians,  e.  g.,  in 
Pseudemys  elegans,  the  pond  turtle  (Figs.  323  and  324)  and  Chely- 
dra  serpentaria,  the  snapping  turtle  (Fig.  325). 


202  ILEO-COLIC  JUNCTION. 

3.  The  ileo-colic  junction  is  provided  with  a  well-developed 
sacculated  csecal  pouch  derived  from  the  proximal  segment  of 
the  colon  and  divided  in  the  interior  by  folds  into  several 
secondary  compartments. 

This  type  is  found  in  some  of  the  phytophagous  lizards,  as 
Iguana  tuberculata  (Figs.  326  and  327).  The  small  intestine  of 
this  animal  is  of  considerable  ^ength  and  of  uniform  caliber  from 
the  pylorus  to  the  ileo-colic  junction.  The  caecum  is  a  large  sac- 
culated pouch  developed  chiefly  along  the  convex  border  of  the 
large  intestine  opposite  to  the  mesenteric  attachment. 

The  examination  of  the  interior  of  this  pouch  reveals  a  compli- 
cated structure  (Figs.  328  and  329).  Fig.  330  shows  the  same 
structures  in  a  closely  allied  form,  Cydura  teres.  The  entrance  of 
the  small  intestine  is  guarded  by  an  annular  sphincter  valve, 
whose  central  circular  opening  leads  into  a  proximal  compart- 
ment of  the  csecum.  This  compartment  is  in  turn  separated 
from  the  remainder  of  the  csecal  pouch  by  a  second  circular  val- 
vular fold  with  central  opening.  Beyond  this  valve  the  interior 
of  the  pouch  carries  a  number  of  crescentic  mucous  folds,  corre- 
sponding to  the  external  constrictions  between  the  csecal  saccula- 
tions. The  entire  pouch  gradually  diminishes  in  caliber  and 
finally  passes  with  a  sharp  angular  bend  into  the  terminal  portion 
of  the  endgut.  At  this  point  the  lumen  of  the  canal  is  slightly 
diminished  by  a  sphincter-like  thickening  of  the  muscularis,  pro- 
ducing an  annular  projection  of  the  mucous  membrane.  The 
entire  csecal  pouch  appears  as  a  specialized  segment  of  the  large 
intestine  interposed  between  the  termination  of  the  midgut  and 
the  terminal  portion  of  the  endgut,  which  latter  is  characterized 
by  uniform  caliber  and  increased  thickness  of  the  muscular  walls. 

The  highly  developed  and  complicated  structure  of  the  csecal 
apparatus  in  Iguana  and  allied  forms  exemplifies  very  clearly  the 
influence  of  vegetable  food  on  the  development  of  this  segment  of 
the  alimentary  tract  when  compared  with  the  simple  type  of  ileo- 
colic transition  found  in  carnivorous  lizards,  as  Heloderma  (Fig. 
322).    Iguana  subsists  on  leaves,  fruits  and  other  vegetable  matter 


ILEO-GOLIG  JUNCTION  IN  BIRDS.  203 

and  the  csecal  pouch  is  invariably  found  filled  with  the  firmer 
and  less  digestible  portions  of  this  food.  These  are  undoubtedly- 
retained  in  the  pouch  by  the  series  of  valves  and  folds  until 
digestion  and  absorption  of  all  available  nutritive  material  for- 
warded from  the  small  intestine  is  completed.  On  the  other 
hand  Heloderma  lives  almost  entirely  on  bird  eggs,  a  concentrated 
and  easily  digested  food.  Consequently  the  ileo-colic  junction 
in  this  lizard  is  exceedingly  simple  and  rudimentary,  marked 
merely  by  a  slight  external  constriction,  with  an  annular  valve 
in  the  interior,  and  an  increase  in  the  caliber  of  the  short  hind- 
gut,  resembling  the  form  found  in  many  teleost  fishes. 

4.  Finally  in  some  Ophidians  a  typical  lateral  csecal  pouch  of 
considerable  dimensions  is  found  connected  with  the  endgut  im- 
mediately beyond  the  ileo-colic  junction. 

An  example  of  this  reptilian  type,  closely  resembling  the  cor- 
responding structure  in  many  Mammalia,  is  presented  by  Eunectes 
marinus,  the  anaconda,  shown  in  Figs.  331  and  332. 

IV.  ILEOCOLIC  JUNCTION  IN  BIRDS. 

In  the  birds  the  length  of  the  intestine  is  subject  to  great  vari- 
ations. The  canal  is  short  in  species  subsisting  on  fruits  and 
insects,  long  in  those  feeding  on  seeds,  plants  and  fish.  The  large 
intestine,  immediately  beyond  the  ileo-colic  junction,  is  provided 
typically  with  two  symmetrical  lateral  cseca  which  extend  in  some 
forms  for  a  considerable  distance  cephalad  on  each  side  of  the 
small  intestine  to  which  they  are  bound  by  peritoneal  con- 
nections. 

As  a  rule  carnivorous  birds  have  short  and  rudimentary  pouches 
(Figs.  333  and  334),  whereas  they  are  long  in  herbivorous  forms 
(Figs.  335  and  336).  Some  carnivorous  birds,  as  Corvus,  Strix, 
etc.,  have  fairly  long  cseca  (Fig.  337).  In  the  passerine  birds 
living  on  seeds  and  insects,  the  caeca  are  of  considerable  length 
as  they  are  also  in  some  of  the  piscivorous  divers  (Figs.  338  and 
339).  They  are  long  in  the  Ratitse,  and  in  the  Lamellirostra, 
who  feed  chiefly  on  plants  (Fig.  340). 


204  ILEO-COLIC  JUNCTION. 

The  enormously  elongated  cseca  of  the  African  ostrich  contain 
a  spiral  fold  of  the  mucous  membrane  in  the  interior  (Fig.  341). 

In  place  of  the  usual  double  avian  caecum  a  single  pouch  is 
found  in  a  few  forms,  namely  in  the  Herons  (Fig.  342). 

In  some  birds  the  small  intestine  is  also  provided  with  a  csecal 
pouch,  the  remnant  of  the  vitello-intestinal  duct  corresponding 
in  its  significance  to  the  occasional  mammalian  diverticulum  of 
Meckel  (Figs.  343  and  344).     (C£  p.  35.) 

V.   ILEO-COLIC   JUNCTION,  C^CUM  AND   VERMIFORM   APPENDIX   IN 

THE  MAMMALIA. 

I.   Subclass:  Ornithodelphia. 

I.  Order :   Monotremata. 

In  many  particulars  the  anatomical  structure  of  these  animals 
reveals  a  close  relationship  to  the  Sauropsida.  They  represent  the 
mammalian  class  in  its  lowest  stage  of  evolution. 

The  ileo-colic  junction  in  all  the  existing  forms  is  direct,  with- 
out angular  bend  at  the  entrance  of  the  small  into  the  large 
intestine.  The  caecum  is  a  long  narrow  pouch,  slightly  dilated 
at  the  extremit}'',  derived  from  the  beginning  of  the  colon  and 
extending  backward  along  the  free  margin  of  the  small  intestine. 
The  csecum  resembles  in  its  general  shape  and  structure  the 
pouches  seen  in  many  birds,  except  that  it  is  unilateral,  while 
the  birds  normally  have  two  symmetrical  cseca.  The  csecum  of 
Ornithorhynchus  anatinus,  the  platypus  or  duck  bill,  is  shown 
in  Figs.  345  and  346,  and  that  of  Echidna  hystrix,  the  spiny  ant- 
eater,  in  Fig.  347.  These  two  animals  represent  the  two  genera 
into  which  the  order  is  divided. 

II.  Subclass:  Didelphia. 

II.    Order:  Marsupialia. 

The  Didelphia  are  represented  by  numerous  species,  which  are 
united  by  certain  common  anatomical  characters  of  the  reproduc- 
tive organs  and  dentition  to  form  the  order  of  the  Marsupialia. 
The  individual  species  included  within  this  order  differ  widely  in 


X 


J 

o 

u 

h 

<: 

J 

?L1 

Oh 

Ll5 

a.  II) 

PLATE    CLXX. 


LARGt    IN- 
TESTINE 


SMALL    IN- 
TESTINE 


LARGE    IN- 
TESTINE 


SMALL   IN< 
TESTINE 


Fig.  338. —  Urinator  lumme,  red -throated 
loon.  Ileo-colic  junction  and  cffica.  (Colum- 
bia University  Museum,  No.  1001.) 


Fig.  337. — Bubo  virginianus,  great  homed  owl.   Ileo-colic 
junction  and  caeca.     (Columbia  University  Museum,  No.  672.) 


PLATE    CLXXI. 


COLON 


Fia.  339.— Merganser  serrator,  red-breasted  merganser.   Ileocolic  junc- 
tion and  caeca.   (Columbia  University  Museum,  No.  1798.) 


LARGE    IN- 
TESTINE 


ILEO-COLIC 

JUNCTION 
AND   C/ECA 


SMALL    IN- 
TESTINE 


Fig.  SiO.—Casuarius  casuarius,  cassowary.     (Columbia  University  Museum,  Xo.  1799.) 


PLATE    CLXXII. 


LARGE    IN- 
TESTINE 


SMALL   IN- 
TESTINE 


Fig.  '3il.—Struthio  africanus,  African  ostrich.     Ileo-colic  junction  and  cseca.     (Columbia  Uni- 
versity Museum,  No.  y^f^.) 


PLATE    CLXXIIl. 


LARGE    INTESTINE 


SINGLE    OECAL    POUCH 


SMALL   INTESTINE 


Fig.  342. — Ardea  virescens,  green  heron.    Ileo-colic  junction 
and  caecum.     (Columbia  University  Museum,  No.  1132  a.) 


X 
o 


PLATE    CLXXV. 


LARGE    IN- 
TESTINE 


SMALL    IN- 
TESTINE 


C>ECUM 


Fig.  345. — Ornithorhynchtis  anatinus,  duck  mole. 
Ileo-colon  and  caecum.  (Columbia  University  Museum, 
No.  1499.) 


LARGE    IN- 
TESTINE 


SMALL   IN- 
TESTINE 


Fig.  3A6.— Ornithorhynchtis  nnaiinus,  duck  mole.   Ileo-colon  and  crecum. 
(Columbia  University  Museum,  No.  1500.) 


PLATE    CLXXVI. 


SMALL  IN-_ 
TESTIN  E 


LARGE    IN- 
TESTINE 


LEO-COLIC 
JUNCTION 


Fig.  347. — Echidna  hystrix,  spiny  ant-eater.     Ileo-colon  and   caecum.      (Columbia   Uni- 
versity Museum,  No.  1501.) 


ileo-cjccal 

FOLD 


—  -  colon 


Fig.  34S. — Didvlphis  rirtjUtiann,  ojxtssum.     lleo-colic  juuctiou  and  caecum. 
(Columbia  University  Museum,  No.  1533.) 


MARSVPIALIA.  205 

habit,  food,  mode  of  locomotion,  etc.,  and  consequently  exhibit 
great  diversity  in  the  structure  of  the  skeletal  and  muscular  sys- 
tems and  of  the  alimentary  canal.  With  the  exception  of  the 
Opossums  inhabiting  the  new  world,  the  families  composing  the 
order  are  confined  to  the  Australian  continent  and  the  adjacent 
islands.  In  respect  to  the  alimentary  tract  in  general  and  the  ileo- 
colic junction  in  particular,  we  are  evidently  dealing  with  a  group 
of  animals  which,  while  they  retain  the  common  characters  above 
indicated  as  uniting  them  in  the  marsupial  order,  yet  have  in  the 
structure  of  their  digestive  canal  adapted  themselves  to  widely 
divergent  conditions  of  food  supply  and  environment.  Conse- 
quently within  the  confines  of  this  single  and  largely  isolated  order, 
we  encounter  nearly  all  the  types  of  csecum  and  ileo-colic  junction 
which  are  found  among  the  remaining  mammalia.  The  group  in  its 
individual  representatives  has  passed,  so  to  speak,  through  the  dif- 
erent  stages  of  development  and  evolution  which,  on  a  very  much 
larger  scale,  are  exhibited  by  the  remaining  mammalian  orders. 
We  can,  independently  of  the  systematic  zoological  classification, 
arrange  the  forms  composing  the  order  under  the  following  types  : 

1.  Forms  with  large  well-developed  simple  cseca,  of  uniform  caliber, 
with  rounded  globular  termination. 

This  type  is  encountered  among  the  herbivorous  Marsupials, 
such  as  the  opossums,  kangaroos  and  wallabys.  Fig.  348  shows 
the  structures  in  Didelphis  virginiana,  the  common  opossum.  Fig. 
349  in  a  small  species  of  opossum  from  Trinidad,  and  Fig.  350 
the  same  parts  in  Halmaturus  derbyanus,  the  rock  wallaby. 

2.  Forms  with  enormously  developed  sacculated  caeca,  coiled  spi- 
rally, with  or  without  additional  convolutions  of  the  proximal  colon; 
the  terminal  portion  of  the  csecal  pouch  diminishes  in  caliber  to  form 
a  pointed  appendage. 

This  type  of  caecum  characterizes  the  Phalangeridx  or  Phalangers 
and  the  Phascolarctidse. 

Examples  are  shown  in  Figs.  351  and  352,  representing  the 
structures  in  Trichosurus  vulpinus,  the  vulpine  phalanger,  and 
Phascolarctos  cinereus,  the  koala. 


206  ILEO-COLIO  JUNCTION. 

3.  Forms  with  simple  cseca  of  moderate  size. 
The  Peramelidx  or  bandicoots. 

Fig.  353  shows  the  ileocoHc  junction,  caecum  and  proximal  seg- 
ment of  the  colon  in  Perameles  nasuta,  the  bandicoot. 

4.  Formes  with  sacculated  short  cseca,  whose  terminal  portion  is 
reduced  to  constitute  a  typical  vermiform  appendix. 

The  caecum  of  the  Pha^colomyidse  or  wombats,  resembles, 
in  its  general  structure  and  in  the  presence  of  a  typical  ver- 
miform appendix,  very  closely  the  corresponding  parts  of 
the  alimentary  canal  in  man  and  the  anthropoid  apes.  Fig. 
354  shows  these  structures  in  Phascolomys  wombat,  the  common 
wombat. 

5.  Forms  with  simple  direct  ileo-colic  junction  without  cascum. 

In  the  purely  carnivorous  Marsupials,  comprising  the  family  of 
the  Dasyuridas,  the  reduction  of  the  csecal  apparatus,  foreshadowed 
by  the  appearance  of  the  distal  rudimentary  segment  as  a  vermi- 
form appendix  in  the  wombats,  has  been  carried  to  the  complete 
elimination  of  the  pouch.  The  ileo-colic  junction  in  these  animals 
is  simple,  marked  externally  by  a  circular  constriction  and  inter- 
nally by  an  annular  valve.  The  colon  forms  a  very  short  terminal 
segment  of  the  alimentary  canal.  The  parts  are  shown  in  Fig.  355 
in  a  typical  representative  of  the  family,  Dasyurus  viverinus,  the 
Tasmanian  devil. 

The  structural  modifications  encountered  in  the  digestive  tract 
of  these  carnivorous  Marsupials  can  properly  be  regarded  as  the 
result  of  their  habitual  diet,  and  we  will  meet  with  analogous  and 
identical  examples  of  csecal  reduction  in  the  typical  Carnivores 
among  the  placental  mammals  (c£  p.  212). 

III.    Subclass:  Monodelphia. 
III.    Order:   Edentata. 
In  all  probability  the  Sloths,  Anteaters  and  Armadillos  compos- 
ing this  order  represent  a  highly  specialized  remnant  of  an  ancient 
group  now  largely  extinct.     In  respect  to  the  ileo-colic  junction  the 
Edentates  may  be  arranged  in  two  groups  which  offer,  within  the 


SYMMETRICAL  TYPE  OF  EDENTATE  ILEO-COLIG  JUNCTION.      207 

limited  number  of  existing  species,  a  very  complete  transitional 
series. 

I.    Symmetrical  Type  of  Ileo-colic  Junction. 

1.  Differentiation  in  caliber,  with  direct  funnel-like  transition  of 
small  into  large  intestine.     No  caecum. 

Beyond  the  ileo-colic  junction  the  caliber  of  the  large  intestine 
increases  gradually.  The  terminal  ileum  is  thus  implanted  into 
the  apex  of  a  funnel  formed  by  the  proximal  segment  of  the 
colon. 

Examples  of  this  type  are  furnished  by  Myrmecophaga  juhata, 
the  great  anteater  (Fig.  356),  and  by  Cholcepus  didactylus,  the  two- 
toed  sloth  (Fig.  357). 

2.  Abrupt  demarcation  of  small  and  large  intestine,  with  median 
transition  of  ileum. 

The  caliber  of  the  intestine  enlarges  rapidly  immediately  be- 
yond the  ileo-colic  junction.  This  form  is  derived  from  the  pre- 
ceding by  the  substitution  of  the  abrupt  ileocolic  transition  for  the 
gradual  funnel-shaped  development  of  the  large  intestine. 

The  type  is  illustrated  by  Tatusia  novemcincta,  the  nine-banded 
armadillo  (Fig.  358),  and  is  also  found  in  two  other  armadillos, 
Tolypeutes  and  Xenurus. 

3.  The  colon  on  each  side  of  the  ileocolic  junction  is  prolonged 
backward  along  the  small  intestine,  forming  two  symmetrical  lateral 
globular  colic  caeca. 

This  type,  which  is  to  be  regarded  as  a  further  development  of 
the  preceding  form,  is  also  found  in  the  armadillos.  Fig.  359 
represents  the  structures  in  Dasypus  sexcinctus,  the  six-banded 
armadillo,  and  a  similar  arrangement  of  the  parts  exists  in 
Chlamydophorus,  another  species  of  armadillo. 

4.  The  csecal  pouches  are  more  completely  differentiated,  com- 
municating with  the  colon  by  a  constricted  neck. 

This  results  in  an  arrangement  which  recalls  the  structure  of 
many  avian  cseca  (cf.  Fig.  337)  and  is  seen  in  the  double  csecal 
pouches  of  Cyclothurus  didactylus,  the  little  ant-eater  (Fig. 
360). 


208  ILEO-COLIC  JUNCTION. 

II.  Asymmetrical  Type  of  Ileocolic  Junction. 
The  second  general  group  of  the  Edentates  is  characterized  by 
the  gradual  development  of  a  single  lateral  asymmetrical  caecum, 
in  place  of  the  median  symmetrical  ileo-colic  transition  found  in 
the  forms  just  considered.  The  species  composing  this  group  thus 
form  a  link  leading  up  to  the  right-angled  accession  of  ileum  to 
large  intestine  and  the  lateral  caecum  characteristic  of  most  other 
mammalia. 

1.  This  type  may  be  considered  as  being  inaugurated  by  the 
form  of  ileo-colic  junction  found  in  the  Manidx  or  Pangolins,  as 
illustrated  by  Figs.  361  and  362,  taken  from  the  long-tailed 
pangolin,  Manis  longicauda.  There  is  no  caecum  and  only  a 
slight  differentiation  in  caliber  between  the  small  and  large  intes- 
tine. The  gut  in  all  the  forms  examined  shows  a  very  character- 
istic bend  at  the  ileo-colic  junction,  being  twisted  into  a  figure  of 
8  and  held  in  place  by  mesenteric  folds. 

2.  The  second  stage,  illustrated  by  Arctopithecus  {Bradypus) 
marmoratus,  the  three-toed  sloth  (Fig.  363),  reveals  a  distinct  in- 
crease in  the  caliber  and  convexity  of  the  large  intestine  oppo- 
site the  mesenteric  border  immediately  beyond  the  ileo-colic 
junction. 

3.  This  leads  in  the  third  stage,  represented  by  Tamandua  bivit- 
tata,  the  Tamandua  ant-eater  (Figs.  364  and  365),  to  the  develop- 
ment of  a  distinct  lateral  caecal  pouch.  I  have  had  no  oppor- 
tunity of  examining  the  structures  in  Oryderopics,  but  from  the 
published  descriptions^  the  large  caecum  of  this  animal  would  form 
the  final  link  in  this  series. 

IV.    Order;   Sirenia. 

Of  the  two  living  representatives  of  this  remarkable  mamma- 
Han  order  the  dugong  [Halicore)  is  described  as  possessing  a  single 
caecum,  while  the  caecal  pouch  of  Manatus  americanus,  the  mana- 
tee, is  symmetrically  bifid  at  the  extremity  (Fig.  366). 

^ Flower  and  Lyddecker,  "Mammals,  Living  and  Extinct,"  p.  209. 


PLATE    CLXXVII. 


LEO-COLIC 
JUNCTION 

DORSAL  VASCU- 
LAR ILEO-CCCAL 
FOLD 


INTERMEDIATE 
NON-VASCULAR 
LEO-OECAL  FOLD 


Fig.  3i9^pidelphis  sp.  ?  opossum.     Ileo-colic  junction  and  caecum.     (Columbia  Univer- 
sity, btudy  Collection.) 


LEO-OCCAL 
FOLD 


Fig.  350. — Halmatunis  derhyanus,  rock  kangaroo.     Ileo-colic  junc- 
tion aud  caecum.     (Columbia  University  Museum,  No.  727.) 


PLATE    CLXXVIII. 


^PvH 

^^^^^^^^^^^^^^K                                   .^'i<        S^^^^^^^^B&^^^^^^^^^^^^^^^^^^^I 

^^^^^^V              '"'j^s^iL  ^^ttf      '^  *!^^9ll^^^^^B    ^^^^^^^^^1 

^^v  ~  ^^^^M^^'QsAJttJI^p^^^^^^l 

^K^  lift.  wJ^MJM 

LEO-COLIC 
JUNCTION 


Fig.  351. —  Trlchosurus  valpinus,  vulpine  phalanger.     lleo-colic  junction 
and  caecum.     (Columbia  University  Museum,  No.  1800.) 


PLATE    CLXXX. 


APPENDIX 


Fig.  354. — Phanculuiiiys  wuiuhat,  wouiljut.     Ileo-ctucum  aiitl  appendix.     (Columbia  Uuivcrsity 
Museum,  No.  1508.) 


ILEO-COUC 
JUNCTION 


Fig.  355. — Dasyurus  viverrinus,  dasyurus,  Tasmanian  devil.     Intestinal  canal.     Ileo-colic 
junction.     (Columbia  University  Museum,  No.  1463.) 


PLATE   CLXXXI. 


ILEO-COLIC 
JUNCTION 


versiTrMSeu^^KmeT '"'"'"'  ^'''' '''''"^'''-    H^o-colic  junction.     (Columbia  Uni- 


LEO-COLiC 
JUNCTION 


~  -   ILEUM 


veTsitl'^^Ienml'SrniT'''*^^'^'  *'^'*-*''^*^  '^"*^-    ileo-colic  junction.     (Columbia  Uni- 


PLATE   CLXXXII. 


Fig.  358.— Tatusia  novemcincta,  niue-bandecl  armadillo.     Ileo-colic  junctiou.     (Columbia  Uni- 
versity Museum,  No.  176.) 


Fig.  359.— Dasypus  sexcindus,  six-banded  armadillo.    Ileo-colic  junction  and  cajca.    (Columbia 
University  Museum,  No.  1478.) 


PLATE    CLXXXIII. 


«n^  ^^''  3'50^,'^ycZo^/iMms-  didactylus,  little  ant-eater.     Ileo-colic  iunction 
and  caeca.     (Columbia  University  Museum,  No.  1512.)  ^""c  Junction 


Fig.  361.— Jfa,jjs  longicanda,  long-tailed  pangolin.     Ileo- 
seum;"  No  95°)'  P^^'P^'-'^tiou.     (Columbia  University  Mu- 


PLATE    CLXXXIV. 


Fig.  362.— Manis  longicauda,  long-tailed  pangolin.    Ileo- 
colic jurction.     (Columbia  University  Museum,  No.  328.) 


PLATE    CLXXXV. 


LEO   COLiC 
JUNCTION 


Fig.  363. — Arctopithecus  marmoratus,  three-toed  sloth.     Ileo- 
colic junction.     (Columbia  University  Museum,  No.  1479.) 


ILEUM    AT 

ILEO-COLIC 

JUNCTION 


Fig.  364. —  T<iiiuiu<hia   b'lr'ittatu,   'raiiiaiulua  ant-eater. 
(Columbia  University  Museum,  No.  l.")90.) 


Ileo-colic  junction   and  csecum. 


PLATE    CLXXXVI. 


GALL- 
BLADDER 


DUCDENO 
COLIC  ISTH 
MUS 


TERMINAL 
BEND  OF 
COLON 


fLEO-COLIC 
JUNCTION 


Fig.  Mo.—  Tamandua  bivittata,  Taniamlua  ant-eater.     Ventral  view  of  abdominal  viscera  from 
the  left  side.     (Study  Collection,  Columbia  University.) 


e  » 


r 

> 

W 
O 

r 

X 
X 
X 
<! 


iOiililliC 


Ifl- 


>. 

y 

a 

C/^ 

> 

1 

a 

Tl 

P 

CO 

n? 

a 

f1 

;*^ 

3 

PLATE    CLXXXIX 


INTERME- 
DIATE ILEO- 
C>ECAL  FOLD 


TERMINAL 

REDUCED 

PORTION 

OF  C/ECUM 


Fig.    '670.— Dicotyle.^   torqnatus,   collared    peccary.      Ileu-colic  juucliou   aud   csBCUm,  isolated. 
(Columbia  University  Museum,  No.  1464.) 


PLATE    CXC. 


Fig.   371. — Capra   oegagrus,   Bezoar  goat.      Ileo-colic  junction  and   caecum,   isolated;    dried 
preparation.     (Columbia  University  Museum,  No.  194.) 


COLONj—  — 


Fig.  372. — Boselaphus  tragocamelus,  nilghai.     Ileo-colic  junction  and  caecum,  isolated.    (Colum- 
bia University,  Study  Collection.) 


PLATE   CXCI. 


OlSTAL   PART 
OF  COLON, 
EMERGING 
FROM  SPIRAk 
PROXIMAL 
SEGMENT 


Fig.  373. — Bos  indicus,  zebu.     Ileo-colic  junction,  caecum,  and  spiral  colon.     (Columbia  Uni- 
versity Museum,  No.  676.) 


Fig.   .374. — Cerrus  silca,  Japanese   deer.      Ileo-colic   junction,    csecum,    and   spiral    colon. 
(Columbia  University,  Study  Collection.) 


PLATE    CXCII. 


DISTAL  SEGMENT 
OF  COLON  EMERG- 
ING   FROM    SPIRAL 


MESENTERY    OF 
SMALL  INTESTINE 


TERMINAL 
ILEUM 


Fig.  375.— Ovis  aries  f(et,  foetal  sheep.     Ileo-colic  junction,  caecum,  and 
spiral  colon.     (Columbia   University  Museum,  No.  1379.) 


DISTAL  SEGMENT 
OF  COLON  LEAV- 
ING   SPIRAL 


PROXIMAL  SEG- 
MENT OF  COLON 
ENTERING  SPIRAL 


Fig.  376. — Oryxleucoryx,  oryx, 
bia  University,  Study  Collection.) 


Spiral  colon,  isolated.    (Colum- 


PLATE   CXCIII. 


TERMINAL    RE- 
DUCED SEGMENT 
OF   OECUM 


DISTAL    SEGMENT 
OF  COLON    BEYOND 
COLIC     LOOP 


PROXIMAL  SEG- 
MENT OF  COLIC 
LOOP 


DISTAL  SEGMENT 
OF  COLIC    LOOP 


Fig.   377. —  Tapirufi  americanus,   American   tapir.     Ileo-colic   junction,    csecum,    and    colon. 
(Columbia  University  Museum,  No.  624.) 


TERMINAL 
COLON 


INTERC/ECAL  SEG- 
MENT  OF    COLON 


PROXIMAL  ILEO- 
COLIC   C/ECUM 


Fig.  378.— Hyrax  syriacus,  hyrax  or  coney.  Intestinal  canal,  with 
ileo-colic  junction,  proximal  ileo-colic  cfecum,  and  distal  paired  colic 
cseca.     (Columbia  University,  Study  Collection.) 


PLATE    CXCIV. 


Fig.  379.— Elephas  indicus,  Asiatic  elephant.     Ileo-colic  junction  and  cjecuui. 
(Columbia  University  Museum,  No.  995.) 


PLATE    CXCV. 


CESOPHAGUS 


\r    .^^^'  ^T^^-~;^2(oa;;«  at;e«aMaH«s,  common  dormouse.     Alimentary  canal.     (Columbia  University 


THE  TWO 
LIMBS  OF 
THE   PROX 
IMAL  COLIC 
LOOP  IMME 
DIATELY   BE 
YOND    THE 
ILEO-COLIC 
JUNCTION 


TERMINAL 
LEUM 


TERMINAL 
REDUCED 
APPENDIC- 
ULAR SEG- 
MENT  OF 
CiCCUM 


Fia381.~Castor  fiber,   heaver.     Ileo-colic  junction,    ciecum,    and    proximal   colon;    ventral 
V.     (Columbia  University  Museum,  No.  1607.) 


PLATE   CXCVI. 


TERMINAL 

REDUCED 

APPENDtC 

ULAR  SEG 

MENT   OF 

CiECUM 


PROXIMAL 
SEGMENT 
OF  COLON 
ENTERING 
COLIC  LOOP 


Fig.  382. — Castor  fiber,  beaver.     Ileo-colic  junction,  caecum,  and  proximal  colon  ;  dorsal  view. 
(Columbia  University  Museum,  No.  1607.) 


> 
o 
X 
o 

u 

h 

< 

Oh 


o  a 


-a 


n3  fl 

cat) 


2o 


M     © 


I 


CI  o 

3   « 

o  o 


,=?  >> 


CO    te 


CD 


<o 


PLATE    CXCVTII. 


APPENDIX 


ILEO-COLIC 
JUNCTION 


SACCUS  LYM- 
PHATICUS 


DISTAL  SEGMENT 
OF  COLON  EMERG- 
ING FROM  SPIRAL 


—  OECUM 


Fig.  385.— Lepus  cuniculus,   rabbit.     Ileo-colic  juuction   and   cajcum.     (Columbia  University 
Museum,  No.  1568.) 


SACCUS  LYM 
PHATICUS 


Fig.  386. — Lepns  ciinicidns,  rabbit.      Ileo-colic  junction    with   saccus   lymphaticus,    isolated. 
(Columbia  University,  Study  Collection.) 


PLATE    CXCIX. 


SPIRAL    MU- 
COUS VALVE 


ILEUM  -  


SACCUS    LYM- 
PHATICUS 


Fig.  387. — Z-e;)!*.?  cjimcM^Ms,  rabbit.  Ileo-colic  junction 
with  saccus  lymphaticus.  Csecuni  and  proximal  segment 
of  colon  opened  to  show  spiral  mucous  fold  in  interior. 
(Columbia  University  Museum,  No.  1587.) 


PLATE    CC. 


SPIRAL    MUCOUS 
FOLD  OF  C£CUV 


MUCOUS    MEM- 
BRANE   OF    AP- 
PENDIX      WITH 
ADENOID 
TISSUE 


Fig.  388. — Lepus  cunicuhis,  rabbit.     Caecum  and  appendix  inverted  to  show  spiral  fold  and 
structure  of  mucosa.     (Columbia  University  Museum,  No.  1588.) 


PROXIMAL 

ENLARGED 
SEGMENT 
OF  COLON 


ILEO-COLIC 
JUNCTION 


DISTAL  SEG- 
MENT OF 
COLON 


Fig.  .iHi). — ]>iix!/proctii  (iijoHli,  a;. 
versity  Museum,  No.  iff g-) 


lUo-colicjinutiou,  caecum,  and  colon.     (Columbia  Uni- 


CETACEAN  AND  UNGULATE  ILEO-COLIC  JUNCTION.  209 

V.    Order :   Cetacea. 

In  the  majority  of  the  whales  the  ileo-cohc  junction  is  simple 
without  caecum,  as  in  Physeter,  Delphinus,  Monodon  and  Phocsena 
(Fig.  367). 

A  few  forms  have  a  small  csecal  pouch. 

VI.  Order;  Ungulata. 
The  intestinal  canal,  in  conformity  with  the  herbivorous  habit 
of  the  group,  is  uniformly  provided  with  a  large  caecum,  and  in 
miany  forms  the  proximal  segment  of  the  colon  immediately  be- 
yond the  ileo-colic  junction  is  more  or  less  extensively  coiled  in  a 
spiral  manner.  This  arrangement  is,  without  doubt,  to  be  regarded 
as  being  functionally  accessory  to  the  caecal  apparatus,  in  the  sense 
of  increasing  very  much  the  area  of  the  secreting  and  absorbing 
surface  and  of  prolonging  the  period  during  which  food-substances, 
which  are  slow  and  difficult  of  elaboration,  are  retained  in  this 
segment  of  the  alimentary  canal. 

1.    Suborder:  Artiodactyla. 

A.  NoN-RuMiNANTiA. — In  the  Suidx  the  caecum  is  large  and  the 
spiral  colon  well  developed  (Fig.  368). 

In  the  peccaries  {Dicotyles)  the  terminal  portion  of  the  caecal 
pouch  is  reduced,  constituting  a  centrally  implanted  appen- 
dage. 

Fig.  369  shows  the  ileo-colic  junction  and  spiral  colon  in 
Dicotyles  torquatus,  the  collared  peccary,  and  Fig.  370  the  caecum 
and  appendix  of  the  same  animal  detached  from  the  spiral  colon. 
In  the  hippopotamus,  on  the  other  hand,  the  caecum  is  said  to  be 
absent.  If  this  is  the  case  the  animal  forms  an  isolated  excep- 
tion among  the  Ungulates. 

B.  RuMiNANTiA. — The  caecum  is  very  large  and  the  spiral  coil  of 
the  colon  extensive. 

Fig.  371  shows  the  caecum  of  Capra  cegagrus,  the  Bezoar  goat, 
detached  from  the  adjacent  intestine,  and  illustrates  the  type  of 
the  ruminant  pouch,  of  considerable  length  and  caliber,  without 

14 


210  ILEO-COLIC  JUNCTION. 

terminal  reduction.     The  same  parts  in  a  preparation  of  Bosela- 
phus  tragocamelus,  the  nilghai,  are  shown  in  Fig.  372. 

Fig.  373  shows  the  caecum  and  ileo-colic  junction,  together  with 
the  spiral  coil  of  the  colon,  in  Bos  indicus,  the  zebu,  and  Fig.  374 
the  same  structures  with  a  typical  example  of  the  spiral  colon 
from  Cervus  sika,  the  Japanese  deer ;  Fig.  375  is  taken  from  a 
preparation  of  the  parts  in  a  foetal  sheep,  while  Fig.  376  shows 
the  spiral  colon  isolated  in  Oryx  leucoryx,  the  oryx. 

2.   Suborder:  Perissodactyla. 

In  the  horse  and  the  rhinoceros  the  csecum  is  very  large  and  of 
uniform  caliber. 

In  the  American  tapir  (Fig.  377)  the  large  csecum  tapers  at  its 
extremity,  to  form  a  species  of  rudimentary  appendix,  resembling 
somewhat  the  corresponding  structure  in  Dicotyles  (cf  Figs.  369 
and  370).  The  proximal  segment  of  the  colon  is  bent  on  itself  in 
the  form  of  an  extensive  loop  with  closely  adherent  limbs,  illus- 
trating an  early  stage  in  the  development  of  the  ruminant  spiral 
colon  (cf  p.233). 

3.    Suborder  :  Hyracoidea. 

This  suborder  is  formed  by  the  single  family  of  the  Hyraddse. 
In  addition  to  their  other  isolated  and  puzzling  structural  pecu- 
liarities the  members  of  this  small  group  present  a  most  unusual 
arrangement  of  the  intestinal  canal,  which  is  unique  among  Uving 
mammalia.  In  addition  to  a  large  sacculated  csecal  pouch,  situ- 
ated in  the  usual  position  at  the  beginning  of  the  colon,  the  large 
intestine  is  provided  further  on  with  two  supplementary  elongated 
pointed  conical  pouches  (Fig.  378). 

This  unique  arrangement,  which  is  not  found  in  any  other 
known  vertebrate,  may  possibly  be  led  back  to  a  type-form 
encountered  in  certain  saurians  (see  p.  234). 

4.    Suborder:  Proboscidea. 
The  C8ecum  of  the  elephant  is  a  very  large  sacculated  pouch 
with  rounded  termination,  illustrated  in  Fig.  379,  taken  from  the 
Asiatic  elephant. 


RODENTTA.  211 

VII.    Order:   Rodentia. 

With  the  exception  of  a  single  group,  the  dormice  (Myoxus) 
(Fig.  380),  the  rodents  possess  a  well-developed  cseeal  appa- 
ratus. 

In  some  forms  the  terminal  portion  of  the  pouch  is  reduced  so 
as  to  constitute  an  appendix.  Many  of  these  animals,  in  addition 
to  the  caecum  proper,  have  the  proximal  colon  elongated  and 
coiled  in  a  spiral,  and  in  some  this  part  of  the  large  intestine  is 
provided  in  the  interior  with  a  spiral  mucous  fold.  This  latter 
structure  functions  again  to  increase  the  extent  of  the  mucous 
absorbing  surface  and  to  prolong  the  retention  of  substances 
undergoing  slow  digestion  and  absorption. 

Typical  examples  of  the  capacious  sacculated  rodent  csecum, 
with  a  terminal  pointed  reduced  segment,  are  afforded  by  Castor 
fiber,  the  beaver  (Figs.  381  and  382)  and  by  Erethizon  dorsatus, 
the  Canadian  porcupine  (Figs.  383  and  384).  Figs.  385  and  386 
show  the  ileo- colic  junction,  caecum  and  appendix  in  Lepus  cunio- 
ulus,  the  rabbit.  The  interior  of  the  csecal  pouch  and  of  the 
proximal  segment  of  the  colon  is  provided  with  a  complete  spiral 
valve  (Fig.  387),  while  the  appendix  is  differentiated  by  the  his- 
tological character  of  its  mucous  membrane  which  is  studded  with 
closely  packed  adenoid  follicles  (Fig.  388) .  A  similar  aggregation 
of  lymphoid  tissue  is  found  in  this  animal  at  the  ileo-colic  junction 
forming  the  s.  c.  saccus  lymphaticus  (Fig.  387). 

The  coils  of  the  proximal  colon  encountered  in  many  rodents  are 
well  seen  in  Dasyproda  agouti,  the  agouti  (Figs.  389  and  390), 
which  animal  also  illustrates  a  type  of  caecum  found  in  several 
members  of  the  order.  The  pouch  here  is  large,  sacculated, 
uncinate,  without  reduction  of  the  terminal  portion. 

The  relatively  enormous  size  of  the  caecum  in  the  Muridse,  is 
shown  in  Fig.  392,  representing  the  entire  visceral  tract  of 
Arvicola  pennsylvanicus,  the  meadow  mouse.  The  pouch  in 
these  animals  is  large,  smooth  and  of  uniform  caliber  (Fig.  393). 

In  some  the  colon  beyond  the  entrance  of  the  small  intestine 
is  provided  with  a  spiral  mucous  valve  (Fig.  394). 


212  ILEO-COLIC  JUNCTION. 

In  the  single  instance  of  Myoxus  among  the  rodents,  the  ileo- 
colic junction  is  simple,  without  any  csecal  pouch  (Fig.  380). 

VIII.  Order:  Camivora. 

A.  PiNNiPEDiA. — In  the  seals  and  walrus  the  csecum  is  very 
small  with  a  blunt  termination.  Fig.  395  shows  its  structure  in 
Zalophus  gillespiei,  Gillespie's  sealion,  and  Fig.  396  in  Phocavitulina, 
the  harbor  seal. 

B.  FissiPEDiA. — The  Cynoidea,  including  the  dogs,  jackals, 
wolves  and  foxes,  form  a  well-marked  central  group  with  well- 
developed  convoluted  caeca  placed  laterally  to  the  ileo-coUc  junc- 
tion (Figs.  397-399). 

From  this  type  depart  on  the  one  hand  the  Ailnroidea,  includ- 
ing the  civets,  ichneumons  and  true  cats,  with  the  csecum  uni- 
formly present,  but  short  and  markedly  pointed,  suggesting  the 
degeneration  of  a  formerly  better  developed  structure  (Figs.  400- 
406),  while  on  the  other  the  Arctoidea,  including  the  bears, 
weasels  and  raccoons,  constitute  a  group  united  by  many  common 
fundamental  peculiarities  of  structure,  among  which  is  the  entire 
absence  of  a  csecal  pouch  (Figs.  407-415). 

Among  the  ailuroid  carnivora,  the  hysena  and  the  lion  occupy 
an  isolated  position  in  regard  to  the  caecum.  Both  of  these 
animals  possess  a  well-developed  long  caecal  pouch  with  blunt 
extremity  (Figs.  416  and  417).  They  probably  afford  examples 
of  a  persistent  ancestral  common  type  from  which  the  remaining 
carnivorous  forms  are  derived  by  reduction  of  the  csecal  apparatus 
in  conformity  with  the  food-habits  of  these  animals.  The  caecum 
of  both  the  lion  and  hyaena  resembles  very  closely  the  pouch 
of  the  herbivorous  marsupials,  such  as  Halmaturus  or  Didelphis 
(cf.  Figs.  348  and  350,  p.  205). 

IX.  Order :   Cheiroptera. 

In  the  bats  the  aHmentary  canal  is  uniformly  simple  without 
caecum  and  scarcely  any  differentiation  between  small  and  large 
intestine  (Fig.  418). 


PLATE   CCI. 


PROXIMAL 

SACCULATED, 

SEGMENT 

OF   COLON 


DISTAL  SPIRAL 
SEGMENT  OF 
COLON 


Fig.  390.— Dasyprocta  agouti,  agouti.    Ileo-colic  jimction,  csecum,  aud  colon.     (Drawing  based 
on  preparation  shown  in  Fig.  388.) 


SECOND  NARROW 

SMOOTH-WALLED 

SEGMENT 

OF   COLON 

PROXIMAL  SAC- 
CULATED   COLON 
SMOOTH  TERMI- 
NAL   SEGMENT 
OF   COLON 


THIRD    SACCU- 
LATED   COLIC 
SEGMENT 
FIFTH    SACCU- 
LATED   COLIC 
SEGMENT 


DIVERTICULUM  OF 


FOURTH 
WALL 


APPENDIX 
ILEO-CiECALIS 


TERMINAL  POR- 
TION OF  OECUM 


Fig    391.— Lagomys  pusillus.     Ileo-colic  junction,   csecum,   and  colon.     (After  Pallas,  from 
Uppel,      Lehrbuch  d.  Vergl.  mikrosk.  Anat.  d.  Wirtelthiere,"  II.,  Jena,  1897,  p.  577,  Fig.  314.) 


PLATE    ecu. 


LIVER 


ILEO-COLIC 
JUNCTION 


Fig.  392. — Arvicola  pennsylvanicus,   field  mouse. 
University  Museum,  No.  815.) 


Alimentary  canal.      (Columbia 


DISTAL  CON- 
STRICTED POR- 
TION OF  COLON 


OECUM 

TRANSITION   OF 
PROXIMAL     EN- 
LARGED     SEG- 
MENT OF  COLON 
INTO    DISTAL 
CONSTRICTED 
PORTION 


Fig.  393.— J/us  decumanus,  white  rat.    Ileo-colic  junction,  caecum,  and  colon.    (Colum- 
bia University  Museum,  No.  1574.) 


PLATE    CCIII. 


COLON  BEYOND 
ILEO-CiECAL 
JUNCTION 
WITH    SPIRAL 
VALVE 


Fig.   394. — Arvicola  riparim,   meadow  mouse.      Ileo-colic  junction, 
csecum,  and  colon.     (Columbia  University,  Study  Collection.) 


Fig.  395. — Zalophns  (jillexpier,  Gillespie's  sea-lion.   Ileo-colic  junction 
and  caecum ;  dried  preparation.    (Columbia  University  Museum,  No.  90.) 


PLATE   CCIV. 


Fig.    396. — Phoea    vitulhm.    harbor    seal.     Ileo-colic   junction  and  caecum. 
(Columbia  University  Museum,  No.  762.) 


PLATE    CCV. 


T.rpJrnVJ^^^"^r''/^'''/'''T''''-'""^^'''^V  H^o-^'-H^  JU"'^tiou  aud  cfficum;  dried 
preparation.     (Columbia  University  Museum,  No.  114.) 


BEGINNING 
OF   CiECUM 


rn  ,  ^i<?-.  398.— CrtMis  familiaris,  dog.      Iko  c<,lic  junction  and  eajcum,  Type  I. 
(Columbia  University  Museum,  No.  1550.) 


PLATE   CCVI. 


Fig.  399.— Canis  familiaris,  dog.  Ileo-colic  juiictiou  aud  ca'cum, 
Type  II.    (Columbia  University  Museum,  No.  1551.) 


Fig.   400.— Genetta  vulgaris,  geiiot.      Ileo-eolic  junction  and 
caecum.     (Columbia  University  Museum,  No.  1625.) 


PLATE    CCVII. 


Fig.  401. — Felis  concolor,   puma.     Ileo-colic  junction  and  csecum ;   dried   preparation. 
(Columbia  University  Museum,  No.  119.) 


Fig.  402. — Fel'iK  i'"ji"<:    "''    lynx.     Ileocolic  junction  and  caecum;    dried 

preparation.     (Columbia  Uuiverbity  Museum,  No.  177.) 


Fig.  403. — Paradoxurus  typns,  paradoxurc.    Ileo-colic  junction  and  caecum;  dried  prepara- 
tion.    (Columbia  University  Museum,  No.  112.) 


PLATE    CCVIII. 


Fig.  404. — Herpestes  sp.  h  ichneumon, 
neo-colic  junction  and  caecum ;  dried 
preparation.  (Columbia  University  Mu- 
seum, No.  120.) 


Fig.  405.— Ferj:)P.s<esgr(.s'eus,  mongoose  ichneu- 
mon. Ileo-colic  junction  and  caecum;  dried 
preparation.  (Columbia  University  Museum, 
No.  149.) 


Fig.  406. — Proteles  lalandii,  aard-wolf. 
(Columbia  University  Museum,  No.  1520.) 


Ileo-colic  junction  and  caecum. 


PRIMATES.  213 

X.  Order:   Insectivora. 

In  the  true  Insectivora  the  caecum  is  also  absent  and  the  ali- 
mentary canal  a  simple  non-differentiated  tube.  -  - 

In  certain  herbivorous  animals  included  in  this  group  on  the 
other  hand,  such  as  Galeopithecus  (Fig.  419),  the  caecum  is  present 
as  an  enormous  sacculated  pouch  with  spiral  convolutions. 

XI.  Order:   Primates. 

The  caecum  is  uniformly  present.     In  certain  of  the  Lemuroidea 

the  terminal  portion  of  the  pouch  is  reduced,  forming  a  species  of 

appendix.     A  typical  vermiform  appendix  is  regularly  found  in 

man  and  in  the  anthropoid  apes,  orang,  gibbon,  chimpanzee  and 

gorilla. 

1.  Suborder  Lemuroidea. 

In  the  typical  lemurs  the  caecum  is  long,  frequently  terminating 
in  a  pointed  appendage.  The  proximal  segment  of  the  colon  is 
looped  and  coiled,  resembling  the  spiral  colon  of  the  Ungulates 
and  Rodents.  Fig.  420  shows  the  caecum  of  Nycticebus  tardigra- 
dus,  the  slow  lemur,  with  the  typical  appendage,  and  Fig.  421 
shows  the  spiral  arrangement  of  the  proximal  colon  immediately 
beyond  the  ileo-colic  j  unction  in  the  same  animal.  Fig.  422,  taken 
from  another  specimen  of  the  same  animal  shows  the  caecum,  ap- 
pendix and  spiral  colon.  Figs.  423,  424,  425  illustrate  the  struc- 
ture of  the  parts  in  three  other  members  of  the  group.  Lemur 
macaco,  Lemur  mongoz  and  Otolicnus  cfrassicaudatus,  all  showing  ter- 
minal reduction  of  the  caecal  pouch  and  tendency  to  spiral  coiling 
of  the  proximal  colon.  In  Tarsius  spectrum  (Fig.  426)  the  caecum 
is  relatively  well-developed,  but  forms  a  simple  pouch  of  uniform 
diameter,  without  terminal  reduction. 

2.   Suborder  Anthropoidea. 

A.    Cynomorpha. 

1.  Cynocephalus. — The  baboons  have  a  well-developed  capacious 

caecum.     The  apex  of  the  pouch  is  usually  blunt  and  rounded, 

or  only  slightly  pointed.     The  caecum  is  sacculated,  conforming 

in  structure  to  the  rest  of  the  large  intestine.     Two  low  vascular 


214  ILEO-COLIC  JUNCTION. 

folds  or  ridges,  a  ventral  and  a  dorsal,  carry  the  ventral  and  dorsal 
caecal  branches  of  the  ileo-colic  artery.  The  intermediate  non- 
vascular fold  is  large,  frequently  fused  with  the  dorsal  vascular 
fold  (cf  p.  264). 

Figs.  427-433  show  the  structures  in  Cynocephalus  sphinx, 
porcarius,  habuin,  anubis  and  in  Cercopithecus  pogonias,  sabseus 
and  campbellii. 

27  Macacus. — The  csecum  is  of  large  caliber,  blunt,  or  in  some 
forms  slightly  pointed  at  the  apex,  sacculated  like  the  colon. 

The  two  vascular  folds  are  narrow  and  low,  studded  with  epi- 
ploic appendages.  The  intermediate  non-vascular  fold  is  large, 
placed  nearer  to  the  dorsal  than  to  the  ventral  vascular  fold. 

Figs.  434-439  show  the  structures  in  Macacus  cynomolgus, 
ochreatus,  rhesus  and  pileatus. 

Fig.  439  is  from  a  formaline  hardened  situs  preparation  of  the 
abdominal  viscera  in  Macacus  cynomolgus,  the  Kra  monkey. 

B.    Arctopithecini. 

The  marmosets  have  a  long  crescen tic-shaped  caecum,  turning 
the  concavity  of  the  curve  upwards  and  to  the  left,  terminating 
in  a  blunt  point. 

Typical  forms  are  shown  in  Fig.  440,  Hapale  jacchus,  Fig.  441, 
Midas  ursulus,  and  Fig.  442,  Midas  geoffrei. 

C.   Cebid^. 

1.  Ateles  and  other  howlers  have  a  large  caecum,  crescentic  in 
shape,  narrowed  at  the  apex,  separated  from  the  colon  by  a  sharp 
and  deep  constriction,  opposite  the  wedge-shaped  ileo-colic 
junction. 

The  ileo-csecal  folds  are  well-developed  and  symmetrical,  two 
equal  vascular  folds,  and  a  free  intermediate  non-vascular  redu- 
plication. 

Types :  Ateles  ater  (Figs.  443-445),  Chrysothrix  sciureus  (Fig. 
447)  and  Nyctipithecus  commersonii  (Fig.  446).  In  Mycetes  (Figs. 
448-450)  the  pouch  is  shorter,  less  curved,  with  a  slight  reduction 
toward  the  less  distinctly  pointed  apex. 


gebidjE.  215 

2.  Lagothrix. — The  csecum  is  very  capacious  and  long,  bent  at  a 
sharp  angle  upwards  and  to  the  left  toward  the  ileo-colic  junction. 

Type  :  Lagothrix  humboldtii  (Fig.  451). 

3.  Pithecia. — The  caecum  resembles  in  general  the  type  pre- 
sented by  Ateles,  but  is  less  curved  and  less  reduced  and  pointed 
at  the  termination. 

Type  :  Pithecia  satanas  (Fig.  452). 

In  general  the  Arctopithecini  and  Ateles,  Mycetes,  Lagothrix  and 
Pithecia  among  the  Cebidse  form  a  group  containing  a  series  of 
csecal  transition  types  which  lead  up  to  the  anthropomorphous 
type,  illustrating  the  following  conditions : 

(a)  The  inherent  crescentic  curve  of  the  caecum,  with  the  con- 
cavity directed  toward  the  left,  and  carrying  the  apex  of  the  pouch 
upward  toward  the  lower  border  of  the  ileum  and  the  ileo-colic 
junction.     {Hapalidae,  Ateles,  Lagothrix.) 

{h)  The  reduction  in  caliber  of  the  terminal  part,  foreshadowing 
by  the  pointed  and  narrow  extremity  of  the  pouch  the  appear- 
ance of  the  appendix  in  the  anthropomorphous  group.  {Hapa- 
lidse,  Ateles.) 

(c)  The  constriction  at  the  level  of  the  ileo-csecal  junction,  with 
the  corresponding  well-marked  differentiation  between  csecum  and 
colon  in  the  interior.     (^Ateles.) 

(d)  The  sharp  bend  in  the  pouch  as  it  makes  its  turn  upward 
and  to  the  left,  repeated  in  certain  types  of  adult  human  cseca  (cf. 
p.  247).     (Lagothrix.) 

(e)  Pithecia  forms  a  transitive  type  between  the  blunt  saccu- 
lated caeca  of  the  Cynomorpha  and  the  curved  pointed  pouches  of 
the  Cebidae,  partaking  of  the  characters  of  both. 

(/)  The  same  character  is  seen  in  the  caecum  of  Mycetes  fuscus 
the  brown  howler  monkey  (Figs.  449  and  450). 

4.  Cebinse. — In  the  typical  genus  Cebus  the  caecum  is  placed 
laterad  to  the  small  intestine  which  is  in  direct  linear  continuity 
with  the  colon.  The  pouch  is  slightly  convoluted  toward  its 
termination,  resembling  in  this  respect  and  in  its  position  relative 
to  the  lumen  of  the  intestinal  canal,  the  disposition  of  the  parts 


216  ILEO-COLIC  JUNCTION. 

in  the  cynoid  carnivora.     Figs.  453  and  454  show  the  structures 
in  two  typical  species,  Cehus  monachus  and  C.  leucophseus. 

D.    Anthropomorpha. 

The  csecum  is  large,  sacculated,  provided  uniformly  with  a 
vermiform  appendix. 

The  pouch  of  the  four  anthropoid  apes  agrees  in  curve,  direc- 
tion, implantation  of  the  appendix  and  the  general  arrangement 
of  the  vascular  and  peritoneal  folds  with  the  structure  in  the 
human  subject. 

1.  Hylobates  hoolock,  Gibbon. — Figs.  455  and  456  represent  re- 
spectively the  ileo-caecum  of  this  animal  in  the  ventral  view,  and 
from  the  left  side  with  the  ileum  turned  forward.  The  caecum  is  a 
globular  rounded  pouch  of  nearly  uniform  diameter,  only  slightly 
enlarged  to  the  right  of  the  root  of  the  appendix  which  arises 
from  its  lowest  part  and  is  pendent. 

(For  arrangement  of  the  ileo-csecal  folds  and  fossse  in  this  form 
see  p.  269.) 

2.  Gorilla  savagei,  Gorilla  (F'ig.  457). — The  csecum  is  large,  dis- 
tinctly sacculated,  presenting  a  decided  curve  with  the  concavity 
directed  toward  the  left.  The  appendix  is  implanted  at  the  center 
of  the  blunt  apex  of  the  pouch,  the  csecal  sacculations  on  each 
side  of  the  root  of  the  appendix  being  of  nearly  equal  size  (folds 
and  fossse,  cf  p.  269). 

3.  Simla  satjrrus,  Orang-outang. — Figs.  458  and  459  represent 
respectively  the  ventral  and  dorsal  views  of  the  caecum  and  ileo- 
colon  in  a  nearly  adult  male  specimen  of  orang,  about  4i  feet  high. 

The  caecum  is  funnel-shaped,  gradually  narrowing  to  the  origin 
of  the  appendix  from  its  apex,  which  is  carried  upwards  to  the 
left  by  the  well-marked  crescentic  curve  of  the  pouch.  The 
sweep  of  the  funnel  to  the  left  and  upwards  is  characterized  by 
the  curved  course  of  the  ventral  longitudinal  muscular  band 
(Fig.  458),  whose  fibers  spread  out  over  a  surface  3  cm.  wide. 
The  apex  is  thus  placed  behind  the  terminal  ileum  close  to  its 
entrance  into  the  large  intestine. 


PLATE    CCX. 


ILEO-COLIC 
lUNCTION 


Fig.  409. — Bassaris asfnfa,  raccoon-fox.    Ileo-colic junction  ;  dried 
preparation.     (Columbia  University  Museum,  No.  289.) 


ILEO-COLlC 
JUNCTION 


Fig.    410. — MtiKteln   sp.  .\    marten.       Ileo-coHc    junction;    dried 
preparation.     (Columbia   University  Museum,  No.  199.) 


PLATE    CCXI. 


ILEO-COLIC 
JUNCTION 


Fig.  411. —  Taxidea  americana,   American  badger.     Ileo-colic  junction;  dried  prepa- 
ration.    (Columbia  University  Museum,  No.  180.) 


ILCO-COLIC 
JUNCTION 


Fig.  412. — Proci/on  lotor,  raccoon.    Ileo-colic  junction  ;  dried  preparation.   (Columbia 
University  Museum,  No.  230.) 


PLATE   CCXII. 


■ 

P 

^ 

i 

t-  — 

1 

COLON 

^Ih 

m 

) 

%■' 

3 

ILEO-COLIC 
JUNCTION 

|B 

w 

^ 

1 

Fig.  U3.—C'ercoleptes  caudivolvulus, 'kin'kaJQa.     Ileo-colic  junctiou  ;  dried 
preparation.     (Columbia  University  Museum,  No.  295.) 


ILEO-COLIC 
JUNCTION 


Fig.   414.— r/rsMs   americanus,    black    bear.       Ileo-colic   junction;     dried 
preparation.      (Columbia   University  Museum,  No.  226.) 


PLATE    CCXIII. 


(LEO-COLIC 
JUNCTION 


Fig.  415. —  Urms  maritimus,  iiolar  bear.     Ileo-colic  junction.     (Columbia  University  Museum, 
No.  748.) 


Fig.  416. — Hi/sena  striata,  striped  hyena.     Ileo-colic  junction  and  csecum ;  dried  preparation. 
(Columbia  University  Museum,  No.  56.) 


PLATE    CCXIV. 


Fig.  417. — Felis  leo,  lion.     Ileo-coHc  junction  and  caecum.     (Columbia  Uuivei-sity  Museum, 
No.  1516.) 


Fig.  418. — Pteropns  medius,  Indian  fruit-bat.  Ileo-colon  ;   dried  preparation.     (Columbia  Uni- 
versity Museum,  No.  533.) 


PLATE    CCXV. 


COLON,   FORM 
ING    A    LOOP 


Univ^ersity  Mi";;e';t;'Nf  l'S4T''"^  ''^"^'-     ^''°"'°'^'  •'""''^°"'  '^'^"^''  ^""^  '"'°^-     (Columbia 


DORSAL   ILEO- 
OECAL   ART. 

INTERMEDIATE 
NON-VASCULAR 
ILEO-OECAL  FOLC 

LARGE    VENTRAL 
VASCULAR    FOLD 
CARRYING    LARGE 
VENTRAL    ILEO- 
C/ECAL  ARTER*' 


onlnJwi  '*~^,-— .-^c^JceJjts  tardigradus,  .sl.nv   leimir.      lUu-colii-  junction,  ciBcum,  appendix,  and 
colon,  doisal  view.     (Columbia  University  Museum,  No.  ^Igs.) 


PLATE    CCXVI. 


Fig.  421. — Nycticebus  tardiiinuhis.  slow  loiiuir.     Same  preparation  as  Fig.  420 ;  ventral 
view,  showing  spiral  coiling  of  proximal  colon.    (Columbia  University  Museum,  No.  tISb) 


COLON 


APPENDIX 


—  CjECUM 


Fig.  422. — Kycticehus  tardigradus,  slow  lemur.     Ileo-colic  junction,  csecum,  appendix, 
and  spiral  colon.     (Columbia  University,  Study  Collection.) 


PHTLOQENY  OF  ILEO-COLIO  JUNCTION  AND  GJSQUM.  217 

At  the  level  of  the  upper  margin  of  the  ileo-colic  junction  the 
narrow  pointed  termination  of  the  caecum  passes  gradually  into 
the  beginning  of  the  appendix  (Fig.  459).  

The  appendix  measures  along  its  free  border  22.6  cm.  It  fol- 
lows the  direction  of  the  csecal  curve  for  2.7  cm.,  at  which  point 
it  appears  somewhat  constricted  and  takes  an  abrupt  bend  down- 
wards for  4.3  cm.;  curving  again  upwards  for  7.5  cm.,  it  turns 
downward  a  second  time  for  5.4  cm.  and  terminates  in  a  hook- 
like extremity  2.7  cm.  long  (Fig.  459). 

4.  Chimpanzee,  Troglodytes  niger. — Figs.  460  and  461  represent 
the  ventral  and  dorsal  view  respectively  of  the  caecum  and  ileo- 
colon  in  a  young  specimen. 

The  caecum  is  curved  to  the  left  and  the  lowest  point  of  the 
pouch  is  formed  by  the  right  lateral  and  ventral  wall  of  the  gut, 
but  the  extreme  crescentic  bend  which  carries  the  origin  of  the 
appendix  up  and  to  the  left  behind  the  ileo-colic  junction  ia 
not  yet  developed  in  the  young  animal ;  on  the  other  hand  this 
character  of  the  caecum  is  typically  apparent  in  Figs.  462  and  463, 
taken  from  an  adult  individual  of  the  same  species. 

This  extreme  curve  is  well  seen  in  the  ventral  view  in  Figs. 
462  and  464,  the  latter  taken  from  a  large  adult  specimen.  Seen 
from  behind  in  Fig.  463  the  sharp  bend  or  kink  in  the  lumen  of 
the  caecal  pouch  produced  by  this  curve  is  striking  and  resembles 
the  arrangement  of  certain  types  of  adult  human  caeca  (p.  247). 

n.  PHYLOGENY    OF    THE   TYPES   OF    ILEO-COLIC    JUNCTION 
AND   CiECUM   IN   THE   VERTEBRATE    SERIES. 

The  segments  of  the  alimentary  canal  illustrate  very  clearly  the 
adaptation  of  structure  to  function.  Diversity  of  kind  and  quan- 
tity of  food  habitually  taken  and  variations  in  the  rapidity  of  tissue 
metabolism  produce  marked  morphological  modifications  in  dif- 
ferent forms.  This  is  more  especially  the  case  with  the  junction 
of  the  mid-  and  hindgut,  the  site  of  development  of  the  caecal  ap- 
paratus and  of  structural  alterations  of  the  large  intestine  possess- 
ing a  similar  physiological  significance.     No  other  portion  of  the 


218  ILEO-COLIC  JUNCTION. 

visceral  tract,  with  the  possible  exception  of  the  stomach,  illus- 
trates more  completely  the  result  of  physiological  demand  on  the 
development  of  anatomical  structure  and  the  morphological  pos- 
sibilities of  departure,  progressive  and  retrograde,  from  a  com- 
mon primitive  type  in  accordance  with  varying  conditions  of 
alimentation. 

In  coordinating,  from  the  morphological  standpoint,  the  struc- 
tural differences  encountered  in  this  segment  of  the  alimentary 
canal,  two  facts  become  apparent. 

1.  In  the  first  place  the  serial  study  of  the  ileo-colic  junction, 
as  we  can  briefly  define  the  region  in  question  by  borrowing  the 
terminology  of  anthropotomy,  reveals  a  limited  number  of  princi- 
pal structural  types  from  which  by  successive  gradations  the  vast 
variety  of  individual  forms  may  be  derived. 

(In  the  schematic  Fig.  465  the  fundamental  types  and  their 
derivatives  are  indicated.  In  the  following  the  individual  forms 
illustrating  these  types  are  referred  to  this  schema  in  brackets.) 

2.  The  observer  will  be  impressed  by  the  fact  that  representa- 
tives of  all  the  main  types  of  ileo-coHc  junction  are  found  within 
a  very  limited  zoological  range,  as  within  the  confines  of  a  single 
order.  Examples  of  this  are  furnished  by  the  Marsupialia  and,  to 
a  lesser  extent,  by  the  Edentata.  The  members  of  these  zoological 
groups,  while  united  by  certain  common  anatomical  characters, 
such  as  the  reproductive  system  and  dentition,  differ  widely  in 
habit  and  in  the  kind  and  quantity  of  the  food  normally  taken. 
These  differences  in  the  method  of  nutrition  have  impressed  their 
influence  on  the  structure  of  the  alimentary  canal  and  have  led 
to  the  evolution  of  varying  and  divergent  types  of  ileo-colic  junc- 
tion. The  study  of  this  segment  of  the  intestinal  tract  can  there- 
fore elucidate  the  mutual  relationship  of  the  vertebrate  groups 
only  to  a  limited  degree  and  in  special  cases.  On  the  other  hand, 
it  renders  very  clear  the  fundamental  structural  ground-plan 
common  to  all  vertebrates  and  accentuates  the  specialized  modifi- 
cations of  this  plan  which  develop  in  response  to  the  physiolog- 
ical environment.     Moreover,  such  a  review  serves  to  reveal  the 


PHYLOQENY  OF  ILEO-COLIC  JUNCTION  AND  CMCUM.  219 

significance  of  rudimentary  and  vestigial  structures,  such  as  the 
human  vermiform  appendix  and  the  serous  and  vascular  folds 
connected  with  the  same.  Throughout  the  entire  vertebrate 
series  the  ahmentary  canal  is  found  to  respond  with  great  readi- 
ness in  its  structure  to  varying  grades  of  functional  demand. 
This  fact  becomes  still  more  apparent  if  the  inquiry  is  not  limited 
strictly  to  the  region  of  the  ileo-colic  junction  but  takes  into 
account  likewise  the  structural  modifications  of  similar  physio- 
logical significance  in  other  segments  of  the  alimentary  tract. 

A  csecal  pouch  or  diverticulum  in  some  form  at  the  junction 
of  mid-  and  hindgut  is  a  very  common  and  widely  distributed 
mammalian  character.  The  activity  of  the  tissue-changes  in 
warm-blooded  animals,  and  the  consequent  necessity  for  a  rapid 
and  complete  digestive  process,  account  for  the  structural  modifica- 
tions of  the  alimentary  tract  so  commonly  encountered  among 
these  forms.  On  the  other  hand,  in  the  lower  cold-blooded  ver- 
tebrates, notably  in  fishes  and  amphibians,  the  metabolism  is 
slow  and  the  alimentary  canal  usually  simple. 

Specifically,  the  caecum  appears  as  a  pouch  or  diverticulum  in 
which  food-substances,  already  partially  digested  and  mixed  with 
the  secretions  of  the  small  intestine,  are  retained  until  their  elab- 
oration is  completed  and  the  nutritive  value  of  the  food  ingested 
is  secured  for  the  organism.  Consequently  the  most  complicated 
and  highly  developed  csecal  apparatus  is  found  among  mammalia 
in  the  Herbivora,  such  as  the  Ungulates  and  Rodents,  whose  food 
contains  a  comparatively  small  amount  of  nutriment  in  ratio  to 
its  bulk,  and  hence  requires  considerable  elaboration  before  absorp- 
tion. On  the  other  hand  the  caecum  appears  as  a  reduced  or  even 
rudimentary  organ,  or  defaults  entirely,  in  Carnivora  whose  food 
is  concentrated  and  easily  assimilated,  containing  only  a  small 
amount  of  non-nutritive  material. 

The  function  of  the  csecal  apparatus  may  be  defined  as 
follows : 

1.  It  provides  space  for  the  retention  of  partly  digested  sub- 
stances, and  of  such  as  are  difficult  of  digestion,  mixed  with  the 


220  ILEO-COLIC  JUNCTION. 

secretions  of  the  preceding  intestinal  segment,  until  the  digestive 
elaboration  is  completed. 

2.  It  increases  the  intestinal  mucous  surface  for  absorption,  and 
may  develop,  in  certain  cases,  special  localized  areas  of  lymphoid 
tissue. 

These  two  functional  characters  may  be  shared  by  other  seg- 
ments of  the  intestinal  tract,  which  undergo  corresponding  struc- 
tural modifications.  It  is  only  necessary  to  refer  in  this  con- 
nection to  the  extreme  morphological  variations  encountered  in 
the  stomach.  The  intestinal  canal  proper,  however,  in  many 
instances  exhibits  structural  peculiarities  which  possess  the  func- 
tional significance  of  the  caecal  apparatus.  Thus  the  projection 
into  the  lumen  of  the  canal  of  a  series  of  mucous  folds,  or  the 
development  of  a  continuous  spiral  mucous  valve,  evidently  serves 
the  double  purpose  of  prolonging  the  period  during  which  the 
intestinal  contents  are  retained,  and  of  increasing  the  intestinal 
mucous  surface  for  absorption. 

This  spiral  mucous  fold  is  encountered  in  the  straight  intestinal 
canal  of  the  Cyclostomata  (Fig.  465,  IV,  1,  and  Fig.  310),  Sela- 
chians (Figs.  466  and  467)  and  Dipnoeans  (Fig.  468).  Phylogeneti- 
cally  it  is  a  very  old  structure,  for  evidences  of  its  existence  are  found 
in  the  fossil  remains  of  some  Elasmobranchs.  In  the  Ostrich  (Fig. 
341)  the  enormously  developed  cseca  possess  the  same  spiral  mu- 
cous fold  in  the  interior.  The  direct  combination  of  the  caecum 
and  spiral  fold  is  again  seen  in  certain  mammalia,  as  in  Lepus  (Fig. 
387).  In  some  Ophidians  the  same  physiological  purpose  is  served 
by  the  manner  in  which  the  convolutions  of  the  long  intestine  are 
bound  together  by  a  subperitoneal  arachnoid  membrane.  The 
lumen  of  the  canal  is  thus  made  to  assume  a  spiral  course  (Figs. 
331  and  469).  The  mucous  folds  of  the  human  intestine,  both 
the  valvulse  conniventes  and  the  crescentic  folds  of  the  large 
intestine,  represent  the  same  spiral  valve,  perhaps  modified  and 
influenced  by  the  erect  posture  of  man  (Figs.  470-475). 

A  second  modification  of  the  intestinal  canal,  suggesting  the 
same  physiological  interpretation  as  the  ileo-colic  caecum,  is  pre- 


/.  SYMMETRICAL  FORM  OF  ILEO-COLIC  JUNCTION.  221 

sented  by  the  so-called  pyloric  caeca  or  appendices  of  many  Teleosts 
and  Ganoids  already  referred  to  (p.  119).  While  these  structures 
in  some  forms  very  probably  have  assumed  a  secretory- function 
(Figs.  476  and  477),  they  evidently  act  in  others  as  diverticula  in 
which  material  undergoing  digestion  is  retained,  while  they  in- 
crease at  the  same  time  the  intestinal  mucous  secretory  and  absorb- 
ing surface  (Figs.  478  and  479).  They  thus  correspond  physiolog- 
ically to  the  ileo-colic  csecum.  In  this  connection  it  is  interesting 
to  note  that  in  Ganoids,  which  possess  both  the  pyloric  appendices 
and  the  spiral  valve,  the  two  structures  develop  in  inverse  ratio 
to  each  other,  indicating  their  functional  identity.  In  the  serial 
review  of  the  structure  and  significance  of  the  vertebrate  caecum 
and  ileo-colic  junction  these  functionally  allied  modifications  of 
other  segments  of  the  intestinal  canal  deserve  notice. 

The  study  of  the  vertebrate  ileo-colic  junction  proper  begins 
both  ontogenetically  and  phylogenetically  with  the  consideration 
of  the  primitive  type  in  which  the  alimentary  tube  is  not  differ- 
entiated into  successive  segments  and  in  which  consequently  no 
distinction  between  mid-  and  hindgut  is  found  (Fig.  465).  An 
example  of  this  primitive  condition  is  presented  by  the  Cyclosto- 
mata,  in  whom  the  alimentary  canal  traverses  the  coelom  cavity 
as  a  straight  non-differentiated  cylindrical  tube.  Fig.  310  shows 
the  alimentary  canal  of  the  Lamprey,  Petromyzon  marinus,  and  it 
will  be  observed  that  the  intestine  is  provided  with  the  spiral 
mucous  fold  above  mentioned. 

From  this  fundamental  type  the  following  main  groups  are  to 
be  derived : 

I.    Symmetrical  Form  of  Ileo-colic   Junction.    Mid-  and   Endgut   in 
Direct  Linear  Continuity.    (Tig.  465,  I.) 

1.  Ileo-colic  junction  marked  externally  by  an  annular  constriction, 
corresponding  to  a  ring-valve  with  central  circular  opening  in  the  in- 
terior (Fig.  465,  /,  1). 

This  form  is  encountered  in  many  Teleosts.  The  projecting 
annular  mucous  fold  resembles  the  pyloro-duodenal  valve. 


222  ILEO-COLIC  JUNCTION. 

Figs.  311-315  illustrate  the  structures  in  representative  Teleosts. 

Among  the  higher  forms  this  type  of  ileo-colic  junction  is  en- 
countered in  the  simple  alimentary  canal  of  many  Amphibians 
(Figs.  318-320).  Among  Reptiles  it  is  found  in  certain  lizards,  as 
in  Heloderma  suspedum,  the  gila  monster  (Fig.  322).  This  animal 
lives  almost  entirely  upon  bird's  eggs,  and  its  simple  and  reduced 
ileo-colic  junction  contrasts  strongly  with  the  highly  developed 
and  complicated  csecal  apparatus  of  the  phytophagous  lizards,  as 
Iguana  (Figs.  326-330),  affording  one  of  the  most  striking  illustra- 
tions of  the  effect  which  the  character  of  the  food  habitually  taken 
has  on  the  structure  of  the  alimentary  canal  in  forms  otherwise 
closely  allied. 

The  same  type  of  ileo-colic  junction,  as  a  reduction  form,  occurs 
in  the  arctoid  group  of  Carnivora  among  Mammalia  (cf  p.  212). 

2.  Differentiation  in  caliber  of  large  and  small  intestine.  Funnel- 
shaped  ileo-colic  transition. 

This  type,  compared  with  the  preceding,  is  characterized  (Fig. 
465,  I,  2)  by  the  greatly  increased  caliber  of  the  large  intestine,  re- 
sulting in  a  funnel-shaped  transition  between  mid- and  hindgut,  the 
small  intestine  continuing  into  the  colon  at  the  apex  of  the  funnel. 

Examples  of  this  type  areipresented  by  several  Edentates,  Myr- 
mecophaga  juhata,  the  great  ant-eater  (Fig.  356),  and  Choloepus 
didadylus,  the  two-toed  sloth  (Fig.  357). 

3.  Abrupt  demarcation  of  small  and  large  intestine  with  caliber 
differentiation  (Fig.  465,  I,  3). 

The  small  intestine  is  still  central  at  the  ileo-colic  junction, 
i.  e.,  the  axis  of  its  lumen  is  continuous  with  the  central  axis  of  the 
colic  lumen.  In  place  of  the  gradual  funnel-shaped  transition  of 
the  preceding  type  the  demarcation  is  abrupt. 

An  example  of  this  form  is  furnished  by  another  Edentate, 
Tatusia  peba,  the  nine-banded  armadillo  (Fig.  358). 

Among  reptiles  a  similar  well-marked  ileo-colic  transition  is 
encountered  in  Alligator  mississippiensis  (Fig.  321). 

4.  Colic  pouch  prolonged  bach  on  each  side  of  the  ileo-colic  junc- 
tion, producing  symmetrical  colic  cssca  (Fig.  465,  /,  4). 


//.    ASYMMETRICAL  FORM  OF  ILEO-COLIC  JUNCTION.  223 

A  growth  of  the  cohc  tube  cephalad,  on  each  side  of  the  junc- 
tion with  the  midgut,  leads  to  the  formation  of  this  type,  charac- 
terized by  the  presence  of  two  symmetrical  globular  csecal  pouches. 
In  its  simplest  form  this  condition  is  illustrated  by  the  double 
colic  cffica  of  another  armadillo,  Dasypus  sexcindus  (Fig.  359). 

The  bifid  csecal  apparatus  of  the  American  manatee  (Fig.  366) 
belongs  to  the  same  group. 

5.  Cxcal  pouches  of  the  birds  (Fig.  465,  J,  5). — A  continuation  of 
the  backward  extension  of  the  bilateral  colic  pouches  leads  to  the 
production  of  the  typical  double  avian  caeca  in  a  greater  or  lesser 
degree  of  development.  Frequently  the  caeca  differentiate  more 
completely  from  the  colon,  appearing  as  pouches  of  varying 
capacity  joined  to  the  large  intestine  by  a  narrower  neck. 

Figs.  334-341  show  the  well-developed  pouches  as  they  appear 
in  representative  avian  types,  while  Fig.  333  illustrates  the  reduc- 
tion of  the  caecal  apparatus  encountered  in  many  carnivorous  birds. 

6.  Among  mammalia  Cydothurus  didactylus  (Fig.  360),  the  little 
ant-eater,  furnishes  an  example  of  double  symmetrical  globular 
caeca,  connected  with  the  colon  by  a  narrow  neck  (Fig.  465,  i,  6). 
Reference  to  the  schema  given  in  Fig.  465  will  show  that  the  types 
heretofore  examined  all  have  the  following  common  character : 

They  appear  derived  from  the  primitive  type  by  a  differentia- 
tion in  the  caliber  of  the  gut  and  by  the  gradual  development  of 
symmetrical  bilateral  caecal  pouches,  resulting  in  central  median 
implantation  of  the  small  intestine  and  its  direct  continuity 
with  the  colon. 

II.   Asymmetrical  Development  of  a  Single  Caecal  Pouch,  Lateral 

I  to  the  Ileo-colic  Junction,  Mid-  and  Endgut  Preserving 

Their  Linear  Continuity.     (Fig.  465,  II.) 
In  the  second  general  group  the  symmetry  of  the  ileo-colic 
junction  is  disturbed.     The  following  types  are  encountered,  form- 
-     ing  a  series  of  successive  stages  : 

1.  The  increase  in  the  caliber  of  the  large  intestine  is  chiefly 
marked  along  the  border  opposite  to  the  mesenteric  attachment, 


224  ILEO-COLIC  JUNCTION. 

resulting  in  a  greater  degree  of  convexity  in  this  part  of  the 
intestinal  wall  (Fig.  465,  II,  1).  Among  Reptilia  this  condition 
is  found  in  the  ileo-colic  junction  of  some  of  the  pond-turtles,  as 
Pseudemys  elegans  (Fig.  323),  while  a  mammalian  example  is  fur- 
nished by  the  three-toed  sloth,  Ardopithecus  marmoratus  (Fig. 
363). 

2.  An  increase  of  this  lateral  extension  of  the  colon  leads  to  the 
formation  of  a  single  lateral  csecal  pouch  (Fig.  465,  II,  2)  such  as 
is  seen  in  another  Edentate,  Tamandua  bivittata  (Fig.  364),  among 
Mammalia,  and  in  certain  Ophidians  among  Reptiles,  as  in  the 
Anaconda  (Figs.  331  and  332). 

3.  Prolongation  of  the  pouch  and  reduction  in  caliber  lead  to 
the  formation  of  the  slender  lateral  csecum  found  in  all  the 
Monotremes  (Figs.  345-347,  Fig.  465,  /,  3).  In  its  general  appear- 
ance the  caecum  of  these  singular  animals  bears  a  close  resemblance 
to  the  csecal  pouches  of  many  birds. 

4.  Direct  continuity  of  small  and  large  intestine,  with  lateral 
colic  caecum,  extending  along  the  convex  free  border  of  the  ter- 
minal ileum  and  slightly  convoluted  at  the  extremity  (Fig. 
465,  II,  4),  characterizes  the  entire  group  of  the  Cehidse,  among  the 
new-world  monkeys.  The  caecum  in  these  animals  is  a  com- 
paratively long  pouch,  nearly  equalling  in  caliber  the  remain- 
der of  the  intestine,  occupying  a  distinctly  lateral  position,  with 
the  terminal  portion  rounded  and  slightly  recurved  (Figs.  453 
and  454). 

5.  The  Cynoid  group  of  Carnivora,  including  the  dogs,  wolves, 
jackals  and  foxes,  presents  a  similar  relative  position  of  small  and 
large  intestine  and  caecum  (Fig.  465,  II,  5).  The  caecum,  compared 
with  that  of  Cebus,  is  longer  and  more  highl}'-  convoluted  (Fig. 
397).  Variations  encountered  in  certain  forms  indicate  rever- 
sions to  a  more  primitive  type.  Thus  Fig.  398  shows  the  usual 
form  in  the  dog,  while  Fig.  399  exhibits  an  occasional  type  in  the 
same  animal.  The  caecum  here  is  less  twisted  and  indicates 
the  probable  derivation  of  the  more  commonly  encountered 
type. 


.     PLATE    CCXVII. 


DISTAL   SEGM 
OF    CO 


PROXIMAL  SEG- 
MENT OF  COLON 


OECUM  WITH    RE- 
DUCED TERMINAL 
SEGMENT 


Fig.  423.— Lemur  macaco,  lemur.  Ileo-colic  junction  and 
caecum.  (Drawn  from  preparation.)  (Columbia  University  Mu- 
seum, No.  1623.) 


■ 


PLATE   CCXVIII. 


OECUM tj 


Fig.  424. — Lemur  moiujoz,  leniiir.  Ileo-colic  junction 
and  cffcum.  (Drawn  from  preparation.)  (Columbia  Uni- 
versity Museum,  No.  1473.) 


PLATE    CCXIX. 


Fig.  426. — Tarsius  spectrum,  spec- 
tre lemur.  (Drawn  from  prepara- 
tion.) (Columbia  University  Mu- 
seum, No.  1521.) 


Fig.  425.— OtolicnuD  crassicaudntus,  galago.  Ileo-colic 
junction  and  caecum.  (Drawn  from  preparation.)  (Colum- 
bia University  Museum,  No.  1626.) 


PLATE    CCXX. 


Fig.  427. — Cynocephalus  sphinx,  Guiuea  baboon. 
(Columbia  University  Museum,  No.  1082.) 


Ileo-colic  junction  and  csecum. 


Fig.  428.— Cynocephnlus   porcarius,  Chacma  baboon, 
caecum.     (Columbia  University  Museum,  No.  1071.) 


Ilco-colic   junction  and 


PLATE    CCXXI. 


Fig.  429. — Cynocephalus  babuin,  yellow  baboon  ;  dried  preparation.     (Columbia  Uni- 
versity Museum,  No.  89.) 


ADHESION  OF 
GREAT  OMEN- 
TUM TO  COLON 


INTERMEDIATE 
NON-VASCULAR 
ILEO-OECAL 
FOLD 


VENTRAL  VAS- 
CULAR   FOLD 


Fig.  •i'iO.—  Cynocei)halus  anubis,  olive  baboon.     (Columbia  Univcrsitj^  Museum,  No.  jfly.) 


PLATE    CCXXII. 


Fig.  431. — Cereopifhcens    puii'mids.    Ixainkd    moiikej'.      Ileo-colic    juuction    aud 
caecum  ;  dried  preparation.     (Columbia  University  Museum,  No.  228.J 


Fig.  432.— Cercopithecus  sabaeun,  green  monkey.     Ileo-colic  junction  aud  csecum. 
(Drawn  from  preparation.)     (Columbia  University  Museum,  No.  7-16.) 

1.  Ventral  ileo-ca?cal  vascular  fold. 

2.  Dorsiil  ileo-ca?cal  vascular  fold. 

3.  Intermediate  ileo-caecal  uon- vascular  fold. 


PLATE    CCXXIir, 


VENTRAL   VAS 
CULAR       FOLD 
FUSING    WITH 
INTERMEDIATE 
NON-VASCULAR 
FOLD    AND    LIM- 
ITING  A   VENTRAL 
ILEO-C>ECfl  L 
FOSSA 


INTERMEDIATE 
NON-VASCU- 
LAR   FOLD 


Fig.  433. — Cercopithecus  campbellii,  cercopithecus  monkey.  Ileo-colic 
junction  and  caecum.  (Drawn  from  preparation.)  (Columbia  University 
Museum,  No.  tH^.) 


Fig.  43-i.—MacacHs  cyuomolgns,  Macaque  monkey.  Ileo-colic  junc- 
It"",!^^  caecum;  dried  preparation.  (Columbia  University  Museum. 
No.  19.)  "^  ' 


■ 


PLATE    CCXXIV. 


Fig.  435. — Macacus  ochreatus,  asliy-black  macaque, 
preparation.     (Columbia  University  Museum,  No.  11.) 


Ileo-colic   junction   and  csecum  ;    dried 


VENTRAL   VAS- 
CULAR   FOLD 


NTERMEDIATC 
NON-VASCU- 
LAR   ILEO- 
CiECAL  FOLD 


Fig.  436. — Macacus  rhesus,  rliesus  monkey, 
versity  Museum,  No.  1126.) 


Ileo-colic  junction  and  csecum.     (Columbia  Lm- 


PLATE    CCXXV. 


VENTRAL  VAS- 
CULAR   FOLD 

NTERMEDIATE 
NON-VASCULAR 
ILEO-OECAL 

FOLD 


h\a  TTni  -l-'' :r-V;""'"'  /^''e«<'«.  macaque.     Iku-clic  jumiiou  and  cscum.    (Colum- 
bia Uuiversity  Museum,  No.  719.) 


rr,  ,  ^i<J-. 4'^8.— Jfacac!ts  mdcus,  bonnet  macaque.    Ileo-colic  junction  and  cs 
(Columbia  University  Museum,  No.  1072.) 


PLATE   CCXXVI. 


GREAT 

OMENTUM 

RAISED 


HEPATIC 

FLEXURE 

OF   COLON 

TRANSVERSE 
COLON 


PANCREAS 


L.    KIDNEY 

FREE    DE- 

SCENDIKG 

MESOCOLON 


Fig.  439.— Macacus  cynomolqns,  kra  monkey.     Abdominal  viscera,  hardened  in  situ.     (Colum- 
bia University  Museum,  No.  1801.) 


PLATE    CCXXVII. 


Fig.   440. — HapuJe   jacchus,    coiumon    marmoset, 
csecum.     (Columbia  University  Museum,  No.  975.) 


Ileo-colic   junction    and 


Fig.  441. — Midas  nrsulus,  negro  tam- 
arin.  Ileo-colic  junction  and  cjEcum; 
dried  pre])aration.  (Columbia  Uuiver- 
.sity  Museum,  No.  2.35.) 


Fig.  442.-  -Midas  (jeoffrei,  Geoffrey's  mar- 
moset. Ileo-colic  junction  and  csecum  ;  dried 
preparation.  (Columbia  University  Museum, 
No.  197.) 


_   Fig.  AAS.—Atdes  afer,  black-faced  coaita.     Ileo-colic  junction  and  csecum : 
dried  preparation.     (Columbia  University  Museum,  No.  240.) 


PLATE   CCXXVIII. 


VENTRAL 

VASCULAR 

ILEO-OECAL 

FOLD 


INTERMEDIATE 
NON-VASCULAB 
ILEO-C/ECAL 
FOLD 

DORSAL   VASCU- 
LAR   ILEO-CiE- 
CAL    FOLD 


Fig.  444.— yKeZes a<er,  black-faced  coaita.   Ileo-colic  junction  and  caecum,  with  ileo-ca'cal 
folds.     (Columbia  University  Museum,  No.  720.) 


PLATE    CCXXIX. 


o^J}l%t^^'7r^*^^^^  f"''  ^^'^ck-faced  coaita.   Ileo-colic  junction  and  ciKcum,  with  ileo- 
caecal  tolds,      (Drawn  from  preparation.)     (Columbia  University  Museum,  No.  300.) 

1.  Ventral  vascular  ileo-cffical  fold.  ' 

2.  Intermediate  non-vascular  ileo-csecal  fold. 

3.  Dorsal  vascular  ileo-CBecal  fold. 


PLATE   CCXXX. 


Fig.  446. — Nyctipithecus  commersonii, 
Vitce  monkey.  Ileo-colic  junction  and 
caecum  ;  dried  preparation.  (Columbia 
University  Museum,  No.  238.) 


Fig.  447. — Chrynothrix  sciuretis,  Viti  mon- 
key. Ileo-colic  junction  and  caecum. 
(Columbia  University  Museum,  No.  1624.) 


Fig.  AiS.—Mi/cetes  cavaya,  black  howler.     Ileo-colic  junction 
and  caecum.     (Columbia  University  Museum,  No.  1136.) 


PLATE    CCXXXI. 


X. 


Fig.  449.—Mycetes   /msc!<s,  brown  howler.     Ileo-colic  junction  and  cfficum, 
with  ileo-csecal  folds ;  ventral  view.     (Columbia  University  Museum,  No.  674.)  ' 
1.  Ventral  vascular  ileo-csecal  fold. 
3.  Intermediate  non-vascular  ileo-csecal  fold. 


Pig.  4.50.— Drawn  from  the  same  preparation  as  Fig.  449  ;  dorsal  view. 

2.  Dorsal  vascular  ileo-csecal  fold. 

3.  Intermediate  non-vascular  ileo-csecal  fold. 


PLATE   CCXXXII. 


VENTRAL  VAS- 
CULAR ILEO- 
CiECAL    FOLD 


INTERMEDIATE 
NON-VASCULAR 
ILEO-C>ECAL 
FOLD 


; OECUM 


Fig.   451. — Lagothnx  humboldtii,    Humboldt's    lagothrix.     Ileo-colic    junction    and    ca'cum. 
(Columbia  University  Museum,  No.  1511.) 


PLATE    CCXXXIII. 


Fig.  452. — Pithecia  s(if(nias,  black  saki   monkey.     Ileo-colic  junction 
and  csecum.     (Columbia  Uuiversily  Museum,  No.  641.) 


Fig.  453. — Cebus  monachus,  capucliin  monkey.     Ileo-colic  junction  and 
csecum ;  dried  preparation.     (Columbia  University  Museum,  No.  26.) 


PLATE   CCXXXIV. 


Fig.  454. — Cebus  leucopluieus,  capuchin    monkey.      Ileo-colic  junction   and   caecum. 
(Columbia  University  Museum,  No.  1467.) 


DORSAL  VAS- 
CULAR FOLD 


Fig.  455. — Hylobates  /loo/ocfc,  hoolock  gibbon.     Ileo-colic  junction  and  csecum ;  ven- 
tral view.     (Drawn  from  Columbia  University  Museum  preparation  No.  1530.) 


PLATE    CCXXXV. 


POINT  OF  FUSION 
OF     DORSAL     VAS- 
CULAR  FOLD  WITH 
INTERMEDIATE 
NON-VASCU- 
LAR   FOLD 


Fig.  456.— Drawn  from  same  preparation   as   Fig.  455 ;    view  from  left  side 
showing  formation  of  posterior  ileo-caecal  fossa.  ' 


VENTRAL  VAS- 
CULAR FOLD 


^^f-'^oV.— Gorilla  savagei,  gorilla.     Ileo-colic  junction  and  caecum,  with  ileo- 
csecal   folds.     (Drawn  from  Columbia  University  Museum  preparation  No.  1543.) 


> 

X 
X 
o 
u 

u 

H 

< 

0. 


.S  fl 


•SS 


oc  S 


PLATE    CCXXXVII. 


Fig.  459. — Simla  satyrus,  orang.  Caecum  and  ileo-colic  junction ;  dorsal  view.  (Drawn 
from  Columbia  University  Museum  preparation  No.  716 J.  1.  Appendix.  2.  Intermediate 
non-vascular  fold. 


Fig.  460. —  Troglodytes  niger,  chimpanzee.  Ileo-colic  junction  and  cajcum  ;  ventral  view. 
(Drawn  from  Columbia  University  Museum  preparation  No.  675.)  1.  Appendix.  2.  Inter- 
mediate non-vascular  ileo-csBcal  fold.     3.  Colon. 


PLATE    CCXXXVIII. 


Fig.  461. — Troglodytes  niger,  chimpanzee.  Dorsal  view.  (Drawn  from  Co- 
lumbia University  Museum  preparation  No.  675.)  1.  Appendix.  2.  Interme- 
diate non-vascular  ileo-csecal  fold.     3.  Dorsal  vascular  fold. 


Fig.  462. —  Troglodytes  niger,  chimpanzee.  Ileo-colic  junction  and  caecum; 
ventral  view.  (Drawn  from  Columbia  University  Museum  preparation  No.  1083.) 
1.  Ventral  vascular  ileo-caecal  fold. 


PLATE    CCXXXIX. 


•     ^^^.•^^■''■~'^'''^<l''^'^!/tesiii{l<'r,(:hm\]ydn'AQe.    Ileo-colic  juuction  and 
View.     (Drawn  from  Columbia  University  Museum  preparation  No.  1083  ) 
1.  Appendix.  '' 


cfecum ;  dorsal 


INTERMEDI- 
ATE NON-VAS- 
CULAR   FOLD 


mrXn^Vrll^'p  r^^K-^^Ti'  •'"^'■1  Chimpanzee.     Ileo-colic   junction  and    cajcum. 
^urawn  trom  Columbia  University  Museum  preparation  No.  1525.) 


PLATE    CCXL. 


Fig.  465.— Schematic  table  of  the  vertebrate  types  of  ilco-colic  junction. 


III.   BECTANQULAB  FOBM  OF  ILEO-COLIC  JUNCTION.  225 

III.  Rectangular  Ileo-colic  Junction  with  Direct  Linear  Continuity  of 
Caecum  and  Colon.     (Fig.  465,  III.) 

The  third  general  group,  to  which  the  large  majority  of 
Mammalia  belong,  is  characterized  in  its  typical  form  by  a 
right-angled  entrance  of  ileum  into  large  intestine  and  by  the 
direct  caudal  prolongation  of  the  colon  into  a  csecal  pouch  of 
nearly  uniform  caliber  with  globular  termination.  The  axes  of 
the  small  and  large  intestine  are  not  in  the  same  line  as  in  the 
two  former  groups,  but  are  placed  nearly  at  right  angles  to  each 
other.  With  this  change  in  the  direction  of  the  main  intestinal 
segments  the  csecum  ceases  to  be  a  lateral  appendage  to  the  canal 
and  appears  as  a  caudal  prolongation  of  the  colon  beyond  the 
ileo-colic  junction  (Fig.  465,  III).  The  type-form  of  this  group 
is  encountered  among  the  herbivorous  Marsupialia,  such  as  the 
kangaroos  and  opossums.  Fig.  350  shows  the  ileo-colic  junction 
and  caecum  in  the  rock  wallaby,  Halmaturus  derhyanus,  and  Fig. 
348  the  same  structures  in  our  common  opossum,  Didelphis  vir- 
giniana.  The  majority  of  the  remaining  mammalian  forms  de- 
pend upon  modifications  of  this  type,  either  in  the  direction  of 
reduction  of  the  csecal  apparatus,  or  of  increased  development 
with  concomitant  structural  changes  of  similar  physiological  im- 
port in  the  proximal  portion  of  the  colon. 

The  following  subdivisions  of  the  general  group  may  be  estab- 
lished. 

A.  1.  The  caecum  is  long,  markedly  curved  or  uncinate,  with 
the  crescentic  medial  margin  turned  toward  the  free  border  of  the 
terminal  ileum.  The  entire  pouch  usually  diminishes  gradually 
in  caliber  to  its  termination  (Fig.  465,  III,  A,  1).  This  type  is 
encountered  in  a  large  group  of  new  world  monkeys,  including  the 
marmosets  and  howlers. 

Fig.  440  shows  the  structures  in  Hapale  jacchus,  one  of  the 
marmosets,  and  Fig.  443  illustrates  the  typical  csecum  of  this 
form  in  Ateles  ater,  the  black-handed  spider  monkey. 
^^     2.  The  caecum  and  appendix  of  man  and  of  the  anthropoid  apes 
^g  can  be  regarded  as  a  reduction  form  of  this  type  (Fig.  465,  ///,  A,  2). 

t 


226  ILEO-COLIC  JUNCTION. 

Arrest  of  development  of  the  terminal  portion  converts  the  distal 
segment  of  the  csecal  pouch  into  an  appendix  whose  relation  to 
the  apex  of  the  funnel-shaped  proximal  segment  or  caecum  proper 
is  seen  in  its  pure  form  in  the  human  embryo  (Figs.  512  and  625). 
AVith  the  further  development  of  the  caecum  the  sharper  demarca- 
tion between  it  and  the  appendix  results  (Figs.  517  and  518).  The 
displacement  of  the  root  of  the  appendix  cephalad  and  to  the  left, 
toward  the  lower  margin  of  the  ileo-colic  junction,  as  it  is  usually 
seen  in  adults,  is  due  to  the  relatively  greater  growth  of  the  right 
terminal  sacculation  of  the  caecum  compared  with  the  left  (cf 
types  of  caeca,  p.  248).  Throughout  these  changes  the  initial  cres- 
centic  curve  of  the  caecum,  turning  its  concavity  upwards  and  to 
the  left,  can  be  recognized  by  tracing  the  course  of  the  longitudinal 
colic  muscular  bands.  The  caeca  and  appendices  of  the  anthropoid 
apes  present  the  same  characters.  The  structures  in  the  orang, 
chimpanzee,  gorilla  and  gibbon  are  shown  in  Figs.  455-464. 

B.  The  iEluroid  and  Arctoid  groups  of  the  Carnivora  and  the 
Pinnipedia  constitute  a  very  complete  and  instructive  series  illus- 
trating the  gradual  reduction  of  the  caecum  from  the  capacious 
pouch  of  the  primitive  type  and  its  final  complete  elimination 
from  the  organism  (Fig.  465,  III,  B). 

In  Hysena  (Fig.  416),  the  large  caecum  with  undiminished  caliber 
of  the  terminal  portion  persists  in  its  full  development,  as  seen  in 
the  Marsupials  furnishing  the  fundamental  type  (Fig.  465,  III). 
The  same  type  of  caecum  is  found  in  the  lion  (Fig.  417),  the  only 
true  cat  in  which  the  caecal  apparatus  has  not  undergone  extensive 
reduction.  Phylogenetically  the  presence  of  a  capacious  and 
uniform  caecal  pouch  in  these  two  animals  is  exceedingly  impor- 
tant and  indicates  that  this  type  of  caecum  represents  the  ancestral 
form  common  to  the  aeluroid  carnivore  group,  which,  in  the  re- 
maining living  representatives,  has  become  reduced  in  response 
to  the  influence  which  the  character  of  the  food  has  on  the  struc- 
ture of  this  portion  of  the  intestinal  canal.  The  two  instances  of 
persistence  of  the  primal  type  are  all  the  more  important  as  excep- 
tions to  the  rule  which  is  otherwise  universal  throughout  the  group. 


CMCUM  OF  THE  JELUROID  AND  ARCTOID  CARNIVOBA.  227 

1.  The  first  example  of  this  reduction  (Fig.  465,  ///,  B,  1)  is 
encountered  in  the  Aard-Wolf,  Proteles  lalandii,  a  near  relative  of 
hyaena  (Fig.  406).  The  caecum  in  this  animal  is  considerably 
shortened,  although  still  of  fairly  large  and  uniform  caliber. 

A  similar  type  of  csecal  reduction  is  encountered  in  the  Pin- 
nipede  Oarnivora.  Fig.  396  shows  the  ileo-colic  junction  and  the 
short  blunt  caecum  of  the  harbor  seal,  Phoca  vitulina. 

2.  The  caecum  of  the  typical  Felidae,  other  than  the  lion,  is  short 
and  the  terminal  portion  much  reduced  in  caliber,  constituting 
in  many  forms  a  species  of  pointed  rudimentary  appendix  (Fig. 
465,  III,  B,  2).  Fig.  401  represents  the  typical  feline  caecum  as 
seen  in  the  puma,  Felis  concolor.  Among  the  smaller  ^Eluroid 
Carnivora  related  to  the  true  cats,  as  the  civets  and  ichneumons, 
the  terminal  reduction  of  the  short  caecum  is  still  more  marked, 
as  seen  for  example  in  Herpestes  griseus  (Figs.  404  and  405). 

3.  In  the  Arctoid  group  of  Carnivora  (Fig.  465,  III,  B,  3  and 
4)  the  reduction  of  the  caecal  apparatus  has  been  carried  to  the 
complete  elimination  of  the  pouch,  restoring  the  primitive  type 
of  a  straight  intestinal  tube  without  diverticulum  as  encountered 
above  in  some  of  the  Edentates  (Figs.  356  and  357). 

In  some  forms  allied  to  the  true  bears,  such  as  Procyon,  Bas- 
saris,    Cercoleptes,  Taxidea   and  Nasua,  the  ileo-colic  junction  is 
marked  externally  by  a  slight  constriction  and  internally  by  the 
projection  of  an  annular  pylorus-like  valve  (Figs.  407-409).     The 
transition  from  the  thin-walled  ileum  to  the  thick  muscular  walls 
of  the  large  intestine  is  abrupt.     The  latter  is  very  short  and 
usually  increases  in  caliber  as  it  approaches  the  anal  orifice.     The 
mucosa  of  the  terminal  ileum  presents  very  commonly  one  or  two 
large  oval  areas  of  agminated  follicles  near  the  ileo-colic  junction. 
The  mucous  membrane  of  the  large  intestine  is  thrown  into  promi- 
j      nent  longitudinal  folds.    Fig.  408  shows  the  intestine  of  the  brown 
coati,  Nasua  rufa,  opened  on  each  side  of  the  ileo-colic  transition. 
IK     In  some  of  the  Arctoidea,  as  Procyon  and  Nasua,  the  beginning 
■^of  the  colon  just  beyond  the  ileo-colic  valve  is  bowed  out  oppo- 
site the  mesenteric   border  indicating  the  original  site  of  the 


228  LARGE  AND  SMALL  INTESTINE. 

eliminated  caecum,  and  recalling  the  arrangement  of  the  intestine 
encountered  above  in  Arctopithecus  among  the  Edentates  (Figs. 
363,  407,  412,  and  465,  III,  B,  3).  Moreover,  in  the  same  forms 
rudimentary  vascular  and  serous  folds  around  the  ileo-colic  junc- 
tion, corresponding  to  similar  structures  found  in  connection  with 
a  well-developed  csecal  apparatus  in  other  mammalia,  point  to  the 
former  existence  of  a  caecum. 

4.  In  the  typical  Ursidse  even  these  remnants  and  traces  of  a 
csecal  pouch  have  disappeared  and  the  intestinal  canal  preserves 
a  uniform  cahber,  without  any  differentiation  of  large  and  small 
intestine  (Figs.  414  and  415,  Fig.  465,  III,  B,  4). 

C.  The  last  subdivision  of  the  third  main  group  contains  forms 
in  which  the  large  uniform  pouch  of  the  primal  type  appears 
moderately  reduced  in  length  and  sacculated,  terminating  either 
in  a  blunt  extremity  or  carrying  a  distal  constricted  and  rudi- 
mentary segment  as  an  appendage. 

1.  The  first  of  these  types  is  encountered  in  the  Old  World  cyno- 
morphous  monkeys.  In  all  of  these  animals  the  csecal  pouch  is 
wide  but  comparatively  short,  of  nearly  uniform  caliber  and  sac- 
culated like  the  rest  of  the  colon,  of  which  it  forms  the  direct  caudal 
continuation  (Fig.  465,  III,  C,  1).  The  terminal  portion  of  the 
pouch  is  usually  blunt,  globular  and  rounded  (Figs.  428,  430  and 
431),  in  a  comparatively  small  number  of  forms  slightly  pointed 
(Figs.  427  and  437). 

2.  In  the  second  group  the  terminal  reduced  portion  persists 
either  as  a  fairly  distinct  appendage,  or  in  the  form  of  a  tapering 
pointed  extremity  into  which  the  csecal  pouch  proper  is  continued 
(Fig.  465,  III,  G,  2).  This  type  is  encountered  in  certain  non- 
ruminant  Ungulates.  An  example  of  the  first  condition  is  fur- 
nished by  the  csecal  apparatus  of  the  peccary  {Dicotyles  torquatus) 
(Fig.  370),  while  the  structures  in  Tapirus  americanus  (Fig.  377) 
illustrate  the  second  form. 


GMCUM  PROPER.  229 


IV.  Caecal  Apparatus  Combined  with  Structural  Modifications  of  the 

Proximal  Colon  of  Similar  Physiological  Significance. 

(Fig.  465,  IV.) 

The  fourth  general  mammalian  group  comprises  forms  in 
which  the  caecal  pouch  is  large,  with  or  without  terminal  ap- 
pendage, while  in  addition  the  large  intestine  develops  structural 
modifications  which  possess  the  general  functional  significance  of 
the  csecal  apparatus.  This  highly  developed  and  complicated 
structure  of  the  alimentary  canal  indicates  that  the  habitual  food 
of  these  animals  is  bulky  and  difficult  of  digestion.  Accordingly 
we  find  the  group  composed  in  main  of  the  majority  of  the  Ungu- 
lates and  Rodents  (with  the  exception  of  Myoxus),  forms  in  which 
the  diet  under  natural  conditions  is  purely  herbivorous.  Other 
mammalian  orders,  however,  also  furnish  representatives  of  this 
type  of  csecal  apparatus,  the  conditions  as  regards  character  and 
quantity  of  food  habitually  taken  corresponding  to  those  encoun- 
tered among  the  Ungulates  and  Rodents.  Thus  the  Phalangers 
among  Marsupials  (Fig.  352),  Galeojpithecus  (Fig.  419)  as  an 
exceptional  form  among  the  Insectivora,  and  certain  lemurs 
among  Primates  (Figs.  420-425)  present  examples  of  a  highly 
developed  and  specialized  type  of  csecal  apparatus. 

The  intestinal  tract  of  these  forms  must  therefore  be  considered 
from  two  points  of  view  : 

I.  The  caecum  proper. 

II.  The  analogous  structural  modifications  of  the  proximal  seg- 
ment of  the  colon. 

I.   C-ffiCUM  PROPER. 
The  pouch  of  the  Ungulates  and  Rodents,  taking  these  forms  as 
IH^e  typical  representatives  of  the  entire  group,  is  usually  of  very 
large  size  compared  with  the  rest  of  the  alimentary  canal.     Two 
types  are  found : 

1.  Large  capacious  smooth  csecal  pouch  of  uniform  caliber 
(Fig.  465,  IV,  2).  This  form  is  met  with  in  the  Muridse  among 
Rodents  and  is  illustrated  in  Fig.  393  showing  the  csecum  of  Mus 


230  ILEO-COLIG  JUNCTION. 

decumanus,  var.  albinus,  the  white  rat.  Fig.  392  represents  the 
entire  aUmentary  canal  of  the  meadow  mouse,  Arvicola  pennsyl- 
vanicus,  and  indicates  the  proportion  which  the  csecal  apparatus 
bears  to  the  remainder  of  the  intestinal  tract.  The  typical  caecum 
of  the  Ungulates  is  shown  in  Fig.  371,  taken  from  Capra  cegagms, 
the  bezoar  goat,  and  in  Fig.  372,  taken  from  a  preparation  of 
Boselaphus  tragocamelus,  the  Nilghai. 

2.  The  csecal  pouch  is  large,  markedly  crescentic  in  shape,  sac- 
culated, or  provided  in  the  interior  with  a  more  or  less  complete 
spiral  valve,  and  reduced  in  caliber  in  the  terminal  segment, 
forming  at  times  a  pointed  appendix  (Fig.  465,  IV,  3).  This  form 
is  encountered  typically  among  certain  Rodents,  as  in  Castor  fiber, 
the  beaver  (Figs.  381  and  382),  and  Erethizan  dorsatus,  the  Cana- 
dian porcupine  (Figs.  383  and  384),  but  is  not  confined  to  this  order. 
Thus  cseca  of  very  similar  structure  are  found  among  the  Marsu- 
pials, as  in  Phascolardos  and  Guscus  (Fig.  352).  In  some  of  these 
forms  the  terminal  reduction  of  the  caecum  is  very  marked,  result- 
ing in  a  long  narrow  segment  of  the  pouch  tapering  to  a  sharp  point. 
It  is  significant  to  note  in  this  connection  that  in  one  member  of 
the  marsupial  order,  the  wombat  {Phascolomys),  this  tendency  to 
terminal  reduction  of  the  pouch  has  led  to  the  development  of  a 
caecum  and  appendix  identical  in  structure  and  arrangement  with 
the  corresponding  parts  of  man  and  the  anthropoid  apes  (Fig. 
354).  This  is  merely  another  illustration  of  the  fact,  evidenced 
throughout  the  entire  vertebrate  series,  that  a  primal  type-form  of 
csecal  apparatus,  in  responding  to  the  conditions  which  influence 
the  development  of  structural  modifications,  will  produce  identical 
specific  types  in  animals  otherwise  widely  separated  in  the  zoo- 
logical series. 

Thus  again  the  form  of  caecum  under  discussion,  found  in 
many  Rodents  and  certain  Marsupials,  is  encountered  in  the  only 
Insectivore  possessing  a  caecum  {Galeopithecus)  (Fig.  419),  and  in 
several  Lemuroidea  among  Primates  (Figs.  420-425). 


PROXIMAL  SEGMENT  OF  THE  COLON.  231 


II.   Structural  Modifications  of  the  Proximal  Segment  of  the  Colon 

Analogous  in  Their  Functional  Significance 

to  the  Osecal  Apparatus. 

IH  In  these  forms,  in  addition  to  the  csecal  apparatus  proper,  cer- 
tain accessory  structural  modifications  of  the  adjacent  large  intes- 
tine are  developed  which  possess  the  physiological  significance  of  the 
csecal  apparatus  in  general,  since  they  serve  to  increase  the  extent 
of  the  intestinal  mucous  surface  and  to  prolong  the  period  during 
which  the  contents  of  the  canal  are  retained  for  elaboration  and 
absorption.  These  modifications,  which  appear  most  fully  devel- 
oped in  certain  Rodents  and  Ungulates,  are  of  two  kinds. 

1.  The  development  of  the  colic  mucous  membrane  in  the 
form  of  a  projecting  fold  or  valve  usually  surrounding  the  lumen 
spirally  (Fig.  465,  IV,  1).  The  significance  and  phylogeny  of  this 
spiral  fold  has  been  considered  above  (cf.  p.  193).  Function- 
ally this  reduplication  must  be  regarded  as  in  general  equivalent 
to  the  csecal  apparatus  proper,  in  producing  an  increased  surface 
for  secretion  and  absorption  and  in  retarding  the  movement  of 
intestinal  contents.  The  csecal  pouch  evidently  acts  as  a  reservoir 
in  which  partly  digested  substances,  mixed  with  the  secretions  of 
the  small  intestine,  are  retained  while  the  slow  processes  of  diges- 
tion and  absorption,  already  inaugurated  in  the  antecedent  seg- 
ment of  the  canal,  are  completed.  It  is  reasonable  to  suppose 
that  the  system  of  projecting  mucous  folds  and  reduplications 
encountered  in  the  colon  beyond  the  caecum  have  a  similar  phys- 
iological import.  Moreover,  in  certain  forms  the  caecum  itself  is 
provided  with  a  similar  spiral  mucous  fold,  as  in  the  instances 
already  mentioned  of  Lepus  among  mammalia  (Fig.  381)  and  of  the 
Ostrich  among  birds  (Fig.  341).  We  have  seen  above  (cf.  p.  193) 
that  the  spiral  intestinal  valve  is  encountered  very  early  in  the 
vertebrate  series,  in  forms  in  which  the  alimentary  canal  is  but 
slightly,  or  not  at  all  differentiated,  short  and  straight  in  its 
course.  In  these  forms  the  evident  purpose  of  the  spiral  fold  is  to 
retard  the  movement  of  the  intestinal  contents  and  to  increase  the 
area  of  the  secretory  and  absorbing  surface.     As  a  structural  mod- 


232  ILEO-COLIC  JUNCTION. 

ification  possessing  this  character  we  saw  the  fold  in  the  Cyclos- 
tomata,  Selachians  and  Dipnoeans  (Figs.  310,  466,  467  and  468)  and 
in  certain  Ophidians  {Python  and  Anaconda,  Figs.  331  and  469). 
Among  Mammals  it  is  found  in  certain  Rodentia  in  two  forms : 

(a)  In  some  of  the  Muridae,  as  Arvicola  (Fig.  394),  the  mucous 
membrane  of  the  large  globular  csecal  pouch  is  smooth,  but  the 
proximal  segment  of  the  colon,  immediately  beyond  the  ileo- 
colic junction,  develops  the  spiral  fold  (Fig.  465,  IV,  2). 

(6)  In  other  forms,  as  in  the  hares  (Fig.  465,  /F,  3),  the  greater 
part  of  the  csecum  carries  a  typical  spiral  fold,  continued  up  to  the 
root  of  the  terminal  appendage  (Fig.  388),  in  which  segment  the 
mucous  membrane  is  devoid  of  folds,  but  studded  thickly  with 
lymphoid  follicles.  Beyond  the  caecum  proper  the  spiral  fold  is 
continued  in  the  opposite  direction  into  the  proximal  segment  of 
the  colon,  which  is  large  and  capacious  and  evidently  shares  both 
the  physiological  and  morphological  characters  of  the  caecum 
proper,  forming  so  to  speak  an  accessory  caecal  chamber.  Beyond 
what  we  thus  might  term  the  caecal  division  of  the  colon  the  large 
intestine  becomes  reduced  in  caliber,  and  the  previously  contin- 
uous spiral  fold  becomes  broken  up  into  separate  semilunar  haus- 
tral  plicae,  corresponding  to  the  superficial  constrictions  between 
the  colic  cells.  In  structure  this  distal  segment  of  the  rabbit  colon 
closely  resembles  the  human  large  intestine  (Fig.  474). 

One  of  the  most  marked  examples  of  this  secondary  modifica- 
tion of  the  colon  is  presented  by  the  intestinal  canal  of  another 
Hodent,  Lagomys  pusiUus  (Fig.  391). 

The  caecum  of  this  animal  is  long,  curved,  provided  with  a  well- 
developed  spiral  fold.  The  terminal  segment  of  the  pouch  is  re- 
duced to  an  appendix,  with  smooth  mucosa  containing  adenoid 
tissue,  as  in  the  rabbit.  A  second  adenoid  appendix,  representing 
the  globular  saccus  lymphaticus  of  the  rabbit,  is  derived  from  the 
caecum  at  the  ileo-colic  j  unction.  The  first  segment  of  the  colon 
beyond  the  ileo-colic  j  unction  is  dilated  and  sacculated,  the  caecal 
mucous  fold  being  prolonged  into  it.  This  is  succeeded  by  a  nar- 
row smooth- walled  second  segment.     The  third  division  of  the 


PLATE   CCXLI. 


PANCREAS 


MtD-GUT, 

WITH    SUB- 

NTESTINAL 

VEIN    AND 

SPIRAL 

VALVE 


FORE-GUT 


STOMACH 


CONTRACTED 
F»VUORIC  SEG- 
MENT   OF 
STOMACH 


Fig.   4(>6. — Squalus  acanthim,  dog-fish.      Alimentary  tract,  spleen,  pancreas.     (Drawn  from 
Columbia  University  Museum  preparation  No.  1405.) 


PLATE    CCXLII. 


STOMACH 


PANCREAS 


SPIRAL  INTES- 
TINAL   VALVE 


Fig.  467.— Galeus  canis,  dog-shark.  Alimentary  tract 
opened,  showing  spiral  intestinal  valve.  (Drawn  from 
Columbia  University  Museum  preparation  No.  1429.) 


PLATE    CCXLIII. 


Fig.  468.— Ceratodus  forsteri,  Australian  lung-fish.     Intestinal 
canal  with  spiral  valve.     (Columbia  University  Museum,  No.  1645.) 


PLATE    CCXLIV. 


SPIRAL  FOLUING  OF 

MUCOSA   RESULTING 

FROM      COILING    OF 

INTESTINE 


P^IG.  469.— Python  molnra.i,  Indian  python.  Mid-gut,  dis- 
tended and  fenestrated  to  show  spiral  course  of  himen. 
(Columbia  University  Museum,  No.  72.").) 


Fig.  470. — Human  small  intestine,  opened  to 
show  valvulse  conniventes.  (Columbia  Univer- 
sity Museum,  No.  1841.) 


Fig.  471. — Human  large  intes- 
tine, showing  colic  taenia  and  plica. 
(Columbia   University  Museum,  No. 

1848.) 


PLATE   CCXLV. 


COLIC  T>CNIA 

(LONGITUDINAL 

MUSCULAR  BAND) 


Fig.  473. — C)/nocephalns  anubis,  olive  baboon.  Large 
intestine,  with  cross-section  showing  colic  tfenia  and 
plicae.     (Columbia  University  Museum,  No.  xff^.) 


Fig.  472. — Human  large  intestine, 
opened  and  in  section,  showing  colic 
plicae.  (Columbia  University  Museum, 
No,  1847.) 


PLATE    CCXLVI. 


Fig.  474.— Comparison  of  portion  of  human  transverse  colon  with  distal  segment  of  rabhit's 
large  intestine,  showing  same  arrangement  of  longitudinal  muscular  bands  (colic  taenia)  and  colic 
sacculations.     (Columbia  University  Museum,  No.  1589.) 


PLATE    CCXLVII. 


Fig.  475. — Felis  leo.  lion.     Large  intestine,  with  transverse  section,  showing  smooth  carni- 
Tore  lumen,  without  sacculations  or  plicae.     (Columbia  University  Museum,  No.  1600.) 


COLLECTING 
TUBULCS 
FORMED    BY 
JUNCTION 
OF  PYLORIC 
C>ECA 


A  n 

Fig.  47(). — Pyloric  Cieca  of  Gadiis  calhirlds,  codlisli.    (Columbia  University  Museum,  No.  1825.) 

A.  Bound  together  by  connective  tissue  and  blood-vessels. 

B.  Dissected  to  show  confluence  of  caeca  to  form  a  smaller  number  of  terminal  tubes  of  larger 
calibre  entering  the  intestine. 


PLATE    CCXLVIII. 


GALL- 
BLADDER 


PYLOniC 
APPENDICES 


ILEO-COLIC 
JUNCTION 


MID-GUT 


END-GUT 

WITH 

SPIRAL 

VALVE 


STOMACH 


—    -     SPLEEN 


Fig.  477. — Alimentary  canal  of  Accipenser  sturio,  sturgeon.  Numerous 
pyloric  caeca  are  bound  together  to  form  a  gland-like  organ. 

In  the  smaller  upper  figure  on  the  left  the  stomach,  mid-gut,  and  pyloric 
caeca  are  seen  in  section,  showing  the  lumen  of  the  latter  and  their  openings 
into  the  mid-gut. 

The  lower  left-hand  figure  shows  the  mid-  and  end  gut  in  section,  the 
latter  provided  with  a  spiral  mucous  valve.  (Columbia  University  Museum, 
Nos.  1826,  1827,  and  1828.) 


PROXIMAL  SEGMENT  OF  THE  COLON.  233 

colon  is  again  dilated  and  sacculated,  followed  by  a  short  fourth 
smooth-walled  section.  A  fifth  stretch  is  again  provided  with 
colic  cells,  beyond  which  the  terminal  segment  continues  of 
uniform  caliber  and  with  smooth  walls  to  the  vent.  The  colon 
therefore  presents  three  distinct  sacculated  portions  whose  struc- 
tural modifications  suggest  that  they  function  in  the  same  sense 
as  the  caecal  pouch  proper.  In  man  and  in  other  Primates  the 
crescentic  colic  plicae  are  disposed  in  a  more  or  less  evident  spiral 
manner  around  the  axis  of  the  intestine,  and  it  is  not  difficult  to 
recognize  in  them  the  modified  remnants  of  the  typical  spiral 
valve  of  lower  forms.  On  the  other  hand,  in  conformity  with  the 
general  reduction  of  the  csecal  apparatus,  the  mucous  membrane 
of  the  large  intestine  in  Carnivora  is  smooth  and  devoid  of  any 
trace  of  the  spiral  fold  (Fig.  475). 

2.  The  second  structural  modification  of  the  large  intestine, 
associated  in  functional  significance  with  the  csecal  apparatus,  de- 
pends upon  the  increase  in  the  length  of  the  proximal  segment  of 
the  colon  beyond  the  ileo-colic  junction  and  the  twisting  or  coiling 
of  this  segment  in  a  more  or  less  complicated  definite  manner,  usu- 
ally in  the  form  of  a  spiral,  the  individual  turns  of  the  coil  being 
held  in  place  by  the  peritoneal  connections.  The  proximal  colon 
thus  modified  is  admirably  adapted  to  retard  the  movement  of 
contents  not  yet  completely  digested  and  to  increase  the  absorb- 
ing surface  of  the  intestine,  and  hence  is  functionally  allied  to 
the  csecal  apparatus. 

This  colic  modification  is  found  in  its  highest  degree  of  devel- 
opment in  the  ruminant  Ungulates,  whose  caecal  pouch  proper  is 
also  enormously  developed.  In  these  animals  the  colon  imme- 
diately beyond  the  ileo-csecal  junction  is  arranged  in  the  form 
of  a  double  spiral,  the  afferent  (csecal)  and  efferent  (colic)  tubes 
alternating,  and  continuous  with  each  other  in  the  center  of  the 
coil  (Fig.  465,  IF,  5).  Examples  of  this  type  of  spiral  colon  are 
shown  in  Fig.  373  {Bos  indicus),  Fig.  374  {Cervus  sika),  Fig.  375 
(Ovis  aries),  Fig.  376  {Oryx  leucoryx).  Ontogenetically  the  com- 
plicated spiral  colon  of  the  ruminants  starts  as  a  simple  loop  of 


234  ILEO-COLIC  JUNCTION. 

the  proximal  colon,  which,  with  the  further  rapid  growth  of  this 
segment  of  the  intestine,  is  bent  to  produce  the  turns  of  the  coil 
as  shown  in  the  schematic  Figs.  480-482.  Phylogenetically  the 
same  gradual  development  can  be  traced  in  the  vertebrate  series. 
Perhaps  the  earliest  tendency  to  structurally  modify  the  intestine 
in  the  direction  named  is  found  in  the  manner  in  which  the  in- 
testinal coils  are  bound  together  by  the  subperitoneal  arachnoid 
in  many  Ophidians  (Fig.  331).  Further  in  the  Manidse  among  the 
Edentates  there  is  no  csecal  pouch,  but  the  intestine  at  the  ileo- 
colic junction  is  twisted  into  a  figure  8  and  held  in  this  position 
by  the  peritoneal  connections  (Figs.  362  and  465,  IV,  4).  In 
certain  Marsupials  with  well-developed  csecal  pouches,  such  as 
PhasGolarctos  and  the  Vulpine  Phalangers  (Figs.  351  and  352), 
the  colon  immediately  beyond  the  ileo-colic  entrance  is  sac- 
culated and  bent  in  the  form  of  a  short  loop.  In  the  tapir 
(Fig.  377),  the  proximal  segment  of  the  colon  forms  a  simple 
loop,  whose  afferent  and  efferent  limbs  are  closely  bound  together. 
The  arrangement  of  the  large  intestine  in  this  animal  illustrates 
the  early  embryonal  stage  in  the  development  of  the  complete 
ruminant  spiral  coil  (cf  Fig.  480). 

The  condition  encountered  in  some  Rodents  presents  a  more 
advanced  stage.  Thus  the  large  intestine  in  the  agouti  {Dasy- 
procta  agouti),  shows  the  development  of  the  spiral  coil  advanced 
as  far  as  the  second  turn  of  the  original  loop  (Figs.  389  and  390). 
It  is  readily  seen  that  continued  growth  of  this  segment  of  the 
intestine  leads  to  the  formation  of  the  complete  colic  spiral  as 
found  in  the  typical  Ungulates. 

The  same  arrangement  of  the  large  intestine  obtains  in  certain 
Lemurs  among  the  Primates.  Thus  the  proximal  colon  ox  the 
Slow  Lemur  {Nydicebus  tardigradus)  is  seen  in  Figs.  421  and 
422  to  present  a  typical  spiral  coil,  and  similar  conditions  are 
encountered  in  other  members  of  the  suborder. 

V.  Csecal  Apparatus  and  Colon  in  Hyrax. 

We  have  left  for  our  final  consideration  the  aberrant  and  unique 
mammalian  type  found  in  Hyrax  (Fig.  378).     In  this  remarkable 


CJSCUM  AND  COLON  IN  HYBAX. 


235 


little  animal  the  large  intestine  develops  a  typical  mammalian 
sacculated  caecum  at  the  ileo-colic  junction,  and  in  addition  is 
provided  further  on  with  two  symmetrical  pointed  lateral  colic 
caeca  of  large  size.  It  is  quite  true  that  this  arrangement  is 
unique  among  Mammalia,  confined  entirely  to  the  members  of 
the  suborder  formed  by  the  single  family  of  Hyrax,  and  that  no 
strictly  analogous  disposition  of  the  alimentary  canal  is  encoun- 
tered in  the  entire  vertebrate  series.  Yet  these  aberrant  structures 
are  possibly  capable  of  explanation,  in  regard  to  the  method  of 
their  development,  by  reference  to  the  csecal  apparatus  of  certain 
phytophagous  saurians,  as  Iguana .  and  Gyclura.  In  these  forms 
(Fig.  326-330)  the  small  intestine  enters  the  colon  somewhat  asymi- 
metrically,  the  opening  being  guarded  by  a  well  developed  annu- 
lar valve. 

The  proximal  segment  of  the  large  intestine  forms  an  extensive 
sacculated  pouch.  If  this  is  opened  (Figs.  328-330)  it  is  seen 
that  the  small  intestine  leads  into  a  compartment  which  is  sepa- 
rated from  the  remainder  of  the  pouch  by  a  valvular  diaphragm 
with  central  circular  opening.  Beyond  this  primary  compart- 
ment the  colic  pouch  is  incompletely  subdivided  by  a  series  of 
gradually  diminishing  crescentic  folds,  corresponding  to  the  exter- 
nal constrictions  between  the  sacculations.  The  entire  pouch 
gradually  diminishes  in  caliber  until  it  passes  with  a  sharp  angu- 
lar bend  into  the  terminal  portion  of  the  endgut.  This  terminal 
segment  is  differentiated  from  the  elongated  colic  pouch  by  the 
greater  thickness  of  its  muscular  walls  and  by  a  slight  annular 
projecting  fold  in  the  interior.  In  considering  the  intestinal  tract 
of  Hyrax  it  is  conceivable  that  the  unique  condition  presented  by 
this  animal  may  be  derived  from  some  type  conforming  in  general 
structure  to  the  reptilian  arrangement  of  the  parts  just  detailed, 
as  indicated  in  the  schematic  Figs.  483-485.  The  proximal  typical 
csecal  pouch  of  Hyrax  would  then  correspond  to  the  similar  colic 
pouch  of  Iguana.  To  explain  the  supplementary  colic  caeca  it  is 
necessary  to  suppose  that  the  transition  of  the  colic  pouch  into  the 
terminal  hindgut  had  become  well  differentiated,  and  that  on  each 


236  ILEO-COLIG  JUNCTION. 

side  of  this  junction  the  colic  tube  had  extended  backwards, 
resulting  in  the  production  of  the  supplementary  bilateral  csecal 
pouches  of  Hyrax. 


I 


PART   IV. 

MORPHOLOGY  OF  THE  HUMAN  C^CUM 
AND  VERMIFORM  APPENDIX. 

Not  only  is  the  anatomy  of  this  portion  of  the  alimentary 
tract  of  great  interest  in  relation  to  the  evolution  of  the  human 
structure,  but  in  addition  the  pathological  and  surgical  impor- 
tance of  the  region  warrants  a  very  careful  study  of  the  caecum 
and  appendix.  This  is  more  especially  the  case  since  a  number 
of  variations  in  the  arrangement  of  the  structures  are  encoun- 
tered. These  departures  from  what  we  consider  the  normal  human 
type  have  an  important  bearing  on  the  development  and  progress 
of  the  pathological  conditions  prone  to  involve  the  appendix.  We 
may  consider  the  subject  under  the  following  subdivisions  : 

I.  DEVELOPMENT  OF  THE  CMCVUL  AND  APPENDIX. 

Much  light  is  thrown  on  the  adult  anatomy  of  the  parts  and 
on  the  origin  of  the  variations  observed  by  the  study  of  their 
embryonic  history.  In  considering  the  factors  which  determine 
the  variations  in  the  position,  size,  and  shape  of  the  appendix  it 
must  be  remembered  that  the  rudimentary  character  of  this 
structure  is  responsible  for  many  of  the  aberrant  conditions 
encountered. 

As  a  part  of  the  general  csecal  pouch  which  persists  in  an  early 
developmental  stage  and  which  we  can  regard  as  destined  for 
further  reduction  and  ultimate  elimination  in  the  course  of  evo- 
lution, the  appendix  shares  with  other  vestigial  structures  a  wide 
range  of  variation.  Consequently  the  study  of  the  development 
of  this  portion  of  the  alimentary  tract  enables  us  to  gain  a  clearer 
view  of  the  primary  arrangement  of  the  structures  and  to  trace 
the  causes  which  are  active  in  determining  the  adult  conditions 
most  frequently  encountered. 

237 


238       MORPHOLOGY  OF  THE  HUMAN  C^CUM  AND  APPENDIX. 

At  the  time  when  the  umbiKcal  loop  of  the  intestine  has 
formed  and  has  begun  to  protrude  into  the  cavity  of  the  um- 
bihcal  cord  (fifth  to  sixth  week),  the  first  indication  of  the  future 
caecum  appears  as  a  circumscribed  thickening  of  the  returning  or 
ascending  Umb  of  the  intestinal  loop  a  short  distance  from  the 
apex  (Figs.  486-488).  This  rudiment  indicates  the  derivation  of 
the  future  definite  intestinal  segments  from  the  elements  of  the 
loop.  The  descending  limb,  apex  (site  of  embryonic  vitelline 
dugt,  Meckel's  diverticulum  of  adult)  and  a  short  succeeding  por- 
tion of  the  ascending  limb  furnish  the  ileum  and  jejunum.  The 
rest  of  the  ascending  limb  develops  into  caecum  and  appendix,  as- 
cending and  transverse  colon.  The  increase  in  the  length  of  the  in- 
testine is  not  uniform.  The  formation  of  convolutions  begins  in 
the  seventh  week  in  the  apex  and  subsequently  in  the  descending 
limb.  By  the  eighth  week  a  considerable  number  of  jejuno-ileal 
coils  have  resulted  from  the  growth  in  length  of  these  parts  of  the 
original  umbilical  loop,  while  the  growth  of  the  segment  which 
furnishes  the  colon  is  at  this  time  still  inconsiderable  (Fig.  489). 
In  the  meanwhile  the  thickening  of  the  tube  which  forms  the 
first  rudiment  of  the  caecum  has  developed  into  a  small  sac-like 
enlargement  of  the  gut,  budding  from  the  left  and  dorsal  aspect 
of  the  ascending  limb,  crescentic  in  shape,  turning  its  concavity 
toward  the  parent  tube.  In  the  majority  of  instances  examined 
the  small  outgrowth  is  packed  closely  between  the  incipient  ileal 
convolutions,  lying  under  cover  of  the  more  prominent  bulging 
coils  of  the  umbilical  protrusion,  between  them  and  a  single  coil 
of  larger  arc  situated  dorsally  and  belonging  to  the  jejunal  or 
proximal  portion  of  the  small  intestine  (Fig,  490).  Fig.  497, 
taken  from  an  embryo  of  11  mm.  cervico-coccygeal  length,  repre- 
sents this  stage  in  the  development  of  the  umbilical  loop.  The 
arrangement  of  the  caecum  which  we  can  assume  as  the  typical 
condition  at  this  stage  and  which  determines  in  part  the  subse- 
quent final  arrangement  of  the  structures,  is  illustrated  by  this 
relation  of  the  caecal  bud  to  the  surrounding  incipient  convolu- 
tions of  the  small  intestine,  with  the  larger  part  of  these  coils 


CHANGES  IN  THE  POSITION   OF  C^CUM.  239 

situated  ventrad  of  the  caecum  and  only  a  single  coil  of  larger 
curve  placed  dorsally  ;  the  csecal  pouch,  derived  from  the  ascend- 
ing limb  of  the  umbilical  loop,  is  situated  between  these  two 
divisions,  turning  its  concave  border  to  the  right  and  embracing 
the  parent  tube.  At  the  time  when  the  human  csecum  first  ap- 
pears as  a  distinct  structure  it  forms  a  small  conical  pouch  with 
blunt  extremity  whose  shape  is  well  illustrated  by  the  caecum  of 
some  of  the  new  world  monkeys,  as  Mycetes  fuscus,  the  brown  howler 
monkey  (Figs.  449  and  450).  The  outgrowth  develops  rapidly  in 
length  and  very  soon  assumes  a  distinct  crescentic  shape,  gradu- 
ally tapering  toward  the  extremity,  a  type  which  is  found  repro- 
duced in  the  caecum  of  Ateles  ater,  the  black-handed  spider 
monkey  (Fig.  443).  There  is  as  yet  no  constriction  or  demar- 
cation separating  the  distal  segment  (future  appendix)  from  the 
proximal  part  (caecum  proper)  but  the  entire  pouch  gradually 
narrows  funnel-like  to  its  termination. 

II.  CHANGES  IN  THE  POSITION  OF  THE  C^CUM  AND  APPEN- 
DIX DURING  NORMAL  DEVELOPMENT,  DEPENDING 
UPON  THE  ROTATION  OF  THE  INTESTINE 
AND  THE   SUBSEQUENT  DESCENT 
OF  THE  CiEOUM. 

The  primary  cause  leading  to  the  rotation  of  the  intestinal 
canal  and  inaugurating  the  successive  stages  which  produce  the 
adult  disposition  of  the  tube  is  to  be  found  in  the  rapid  increase 
in  length  of  the  small  intestine.  Numerous  convolutions  of  this 
tube  succeed  to  the  few  primary  coils  noted  in  the  first  stages. 
This  condition  is  illustrated  in  Fig.  498,  taken  from  an  embryo 
of  4.4  cm.  cervico-coccygeal  measure,  and  the  arrangement  of  the 
intestine  is  indicated  in  schema.  Fig.  491.  The  caecum  is  found 
nearly  in  the  median  line  imbedded  among  the  surrounding  coils 
of  the  small  intestine,  which  by  their  rapid  increase  have  pushed 
the  pouch  cephalad  nearly  into  contact  with  the  caudal  surface 
of  the  liver. 

Three  main  divisions  of  the  convolutions  of  the  small  intestine 
can  be  made  out,  slightly  separated  from  each  other  in  the  figure 


240        MORPHOLOGY  OF  THE  HUMAN  C^CUM  AND  APPENDIX. 

to  exhibit  the  csecum  between  them.  The  proximal  (jejunal)  set 
of  these  convolutions  occupy  the  upper  and  left  part  of  the  ab- 
dominal cavity.  They  are  the  product  of  the  single  larger  coil 
which  in  the  earlier  stage  (Fig.  497,  schema  Fig.  490)  appeared 
dorsad  of  the  csecal  diverticulum.  The  distal  (ileal)  division  of 
small  intestinal  convolutions  has  become  greatly  augmented  and 
lies  to  the  right  of  the  caecum.  The  concavity  of  the  pouch  is 
still,  as  in  the  earlier  stages,  directed  to  the  right  and  the 
entrance  of  ileum  into  colon  takes  place  from  right  to  left. 
The  caudal  part  of  the  abdominal  cavity  is  occupied  by  an  in- 
termediate set  of  transition  convolutions  which  join  the  proxi- 
mal and  distal  divisions.  In  the  two  stages  just  described  (Figs. 
497  and  498,  Schema  Figs.  490  and  491),  the  initial  step  in 
the  intestinal  rotation  has  been  taken,  i.  e.,  the  beginning  of  the 
colon  has  been  displaced  cephalad  from  its  original  position  in 
the  caudal  and  left  part  of  the  abdominal  cavity  by  the  pressure 
of  the  rapidly  growing  coils  of  the  small  intestine  and  now 
lies  transversely  ventrad  of  the  duodenum,  having  crossed  the 
duodenocolic  neck  or  isthmus  of  the  primitive  umbilical  loop 
(cf  Fig.  487,  C). 

At  first  the  distal  coils  of  the  small  intestine  occupy  a  position 
behind  as  well  as  to  the  right  of  the  caecum,  forming  a  dorsal  retro- 
caecal  division  connected  by  intermediate  convolutions  with  the 
ventral  division  occupying  the  lower  and  left  portion  of  the 
abdominal  cavity.  The  apex  of  the  caecum  is  frequently  imbedded 
among  these  terminal  coils  of  the  ileum.  With  the  continued 
growth  of  the  small  intestines  a  further  displacement  of  the  caecum 
cephalad  and  to  the  right  takes  place,  while  at  the  same  time  the 
terminal  ileal  coils  pass  downwards  and  to  the  left,  from  a  retro- 
caecal  into  a  subcaecal  position,  thus  permitting  a  direct  apposi- 
tion of  the  caecum  to  the  dorsal  parietal  (prerenal)  peritoneum. 
The  last  steps  in  this  process  of  withdrawal  of  the  original  volu- 
minous dorsal  (retro-caecal)  division  of  ileal  convolutions  are  well 
seen  in  the  preparation  shown  in  Fig.  499,  taken  from  an  embryo 
of  6.7  cm.  vertex-coccygeal  measure,  and  corresponding  to  the 


PLATE    CCXLIX. 


PYLORUS  r-     —     —    — 


Fig.  478. — Stomach,  duodenum,  and  pyloric  caeca  of  Lophins  piscatorius,  angler. 
(Columbia  University  Museum,  No.  1824.) 


MID-GUT 

PYLORIC  C>ECA 

BILE-DUCT 


CESOPHAGUS 


STOMACH 
PYLORUS 


Fig.  479. — Pleuronectes  macnlatus,  window-pane.  Stomach  and  mid- 
gut with  pyloric  cseca  and  hepatic  duct.  (Columbia  University  Museum, 
No.  1432.) 


o 
o 


^      Eh 


PLATE   CCLI. 


Fig.  485. 

Figs.  483-485.— Schematic  figures  illustrating  possible  Hue  of  derivation  of  aberrant  mamma 
lian  type  ot  alimentary  canal  encountered  in  Hyrax. 


PLATE    CCLIL 


EPIGLOTTIS- 


HYPOPHYSIS- 


W§1 

— STOMACH 

^MB 

HEPATIC_ 

w^ 

y— PANCREAS 

DUCT 

%£^^_y^ 

%(■ 

C>ECUM~ 

w  V  M~ 

WOLFFIAN 

INTESTINAL—/ 
LOOP            ' 

K^^^^^ 

■^jfi?^ 

yi 

DUCT 

ALLANTOIC 

.^^1  d 

:      jf 

DUCT 

r^  1 

URINARY 

¥^#7 

jm^ 

BLADDER 

GENITAL    PRO- — 

L      / 

If  '  n  L 

W^^tJ 

RENAL   BUD 

TUBERANCE 

/-^^^ 

^.<^C^ 

Jf 

CAUDAL    END_^ 

L    v'""^ 

^^D%^ 

0^ 

OF  VERTEBRAL 
COLUMN 

^           N^Sfel^tj. 

^'#>i 

CAUDAL   GUT 

Fig.  486. — Alimentary  canal  and  appendages  of  human  em- 
bryo of  12.5  mm.     X  12.     (Kollmann,  after  His.) 


PLATE    CCLIII. 


OESOPHAGUS 


DORSAL      MESOGASTRIUM 


VENTRAL    MESOGASTRIUM 

DUODENUM 

SUPERIOR    MESENTERIC 
ARTERY 

DUODENO-COLIC 
ISTHMUS 
ART.    COLICA    MEDIA 


Fig.  487. — A,  schematic  representiition  of  alinieutary 
canal,  with  umbilical  loop  and  mesenteric  attachments  in 
human  embryo  of  about  six  weeks.  B  and  C,  sta,ges  in  the 
intestinal  rotation. 


PLATE   CCLIV. 


Fig.  488. 


Fig.  489. 


Fig.  490. 


Fig.  491.  Fig.  492. 

Figs.  488-496.— Series  of  schematic  figures  illustrating  stages  in  the  rotation  of  the  intestinal 
canal. 


PLATE    CCLV. 


Fig.  493. 


Fig.  494. 


canal. 


Fig.  495.  Fig  496 

Figs.  488-496.-Series  of  schematic  figures  illustrating  stages  in  the  rotation  of  the  intestinal 


PLATE    CCLVI. 


DESCENDING 
LIMB     OF    IN- 
TESTINAL 
LOOP 


ASCENDING 
LIMB    OF    IN- 
TESTINAL 
LOOP 


EXTRA-UMBIL- 
ICAL   COILS 


DESCEND- 
ING COLON 


POST-OECAL 
COILS 


Fig.  497. — Human  embryo  of  11  mm  cervico-coccygeal 
measure.  Enlarged  view  of  ventral  and  left  aspect  of  intes- 
tinal canal.     (Columbia  University,  Study  Collection.) 


DISTAL (dor- 
sal) COILS 


INFERIOR  INTER- 
MEDIATE   COILS 


PROXIMAL  (ven- 
tral)   COILS 


Fig.  498. — Human  embryo  of  4.4  cm.  cervico-coccygeal  measure.     Intestinal  canal ; 
Liver  removed.     (Columbia  University,  Study  Collection.) 


PLATE    CCLVII. 


DORSAL  fRETRO- 

OECAL)     COIL 

OF      ILEUM 


CONNECTING    CON- 
VOLUTION      BETW   

DORSAL    AND  VEN-         i 
TRAL   COILS 


V  |«     VENTRAL   fPR 


RE- 
-OCCALl    COILS 
OF    ILEUM 


Fig.  499. — Human  embryo  of  6.7  cm.  vertex-coccygeal  measure.     Liver 
removed.     (Columbia  University,  Study  CoUectioii.) 


DISTAL    fDORSAL)       ! 
ILEAL   COILS      T 


PROXIMAL 

1 (VENTRAL) 

'     '     COI 


Fig.  500. — Human  embryo  of  4.9  cm.  vertex-coccygeal  measure.     Ventral  view  of  abdominal 
cavity,  with  liver  partially  removed.     (Columbia  University,  Study  Collection.) 


TERMINAL 
ILEAL  COILS 


Fifi.  501. — The  same  embryo  represented  in  Fig.  500.     The  colic  coil  further  depressed  and 
tunied  to  the  left;  seen  from  the  right  side. 


PLATE    CCLVIII. 


<,r-STOMACH 


DUODENO- 
JEJUNAL 
JUNCTION 


Fig.   502. — Human    embryo,    (i.G    cm.    vertex-coccygeal    measure. 
Liver  removed.     (Columbia  Uuiversity,  Study  Collection.) 


—DUODENUM 


TERMINAL 
ILEUM 


Fig.  50:3.— Human  embryo,  7.6  cm.  vertex-coccygciil  measiiii'.  Liver  and 
small  intestine  from  the  duodeno-jejunal  to  the  ileo-colic  junction  removed. 
(Columbia  Uuiversity,  Study  Collection.) 


PLATE    CCLIX. 


ASCENDING 
COLON 


DUODENO- 

JtJUNAL 

JUNCTION 


TERMINAL 
ILEUM 


Fig.  504.— Human  foetus,  10.6  cm.  vertex-coccygeal  measure.  Liver  and 
greater  part  of  small  intestine  removed.  (Columbia  Uuiversity,  Study  Col- 
lection.) 


R.    KICNEY 


ASCE-NDING 
COLON 


OMEGA 
LOOP 


Fig.  505  —Human  foetus,  20.4  cm.  vertex-coccygeal  measure.     (Columbia 
university,  fetudy  Collection.) 


X 

J 
u 
o 

Id 
h 
< 

0, 


la" 


u 


>  a 
a  ^ 


5'° 


I  u.  t 


PLATE    CCLXI 


HEPATIC 
FLEXURE 


Pig.  508.— Human  foetus oi  :  ..  . .,,.  vertex-coccvgeal  measure.  Liver 
and  small  intestine  from  tlie  duodeno-jejuiial  to  the  ileo-colic  junction 
removed.  The  colon  already  j.re.sents  an  ascending,  transverse  and 
descending  segment.  The  appendix  is  retro-csecal,  curved,  with  the  tip 
turned  dovvn,  under  cover  of  the  ileo-colic  junction  and  mesentery. 
(Columbia  University,  Study  Collection.) 


lid  lie 

Fir,.  .")()<).  — Schematic  table  of  types  of  human  ca-ca. 


P  LATE    CCLXII. 


J 


-^ft^ 


Fig.  310. — Human  fcetiis  at  term.     C'cecum  and  ileo-colic  junction ; 
ventral  view.     (Coluni))ia  Univei-sity,  Study  Collection.) 

1.  Appendix. 

2.  Reduced  intermediate  non-vascular  fold. 

3.  Ventral  va.scular  fold. 


=% 

t       j 

(l      '^ 

."••■[.f^ 

i 

N 

■^l^^00^'-'Z 

i.       ^ 

]•  k;.  511.— Human  foetus  at  term.  Cfecuni  and  ileo- 
colic junction  ;  ventral  view.  (Columbia  University, 
Study  Collection.) 

i.  Appendix,  coiled  spirally  behind  terminal  ileum. 
2.  Non-vascular  intermediate  fold. 


I 


PLATE    CCLXIII. 


r 


APEX   OF  C/ECUM, 
ORIGIN     OF    AP- 
PENDIX 


Fig.   512. — Human    foetus  at  term   (negro). 
(Columbia  University  Museum,  Xo  692.) 


Caecum  and  ileo-colic  junction  ;    ventral  view. 


Fig.  oi:5.^Hunmn  foetus  at  term.  Ca;cum 
and  ileo-colic  junction  ;  dorsal  view.  (Columbia 
University,  Study  Collection.) 


Fig.  514. — Human  foetus  at  term. 
Csecumand  ileo-colic  junction  ;  dorsal  view. 
(Columbia  University  Museum,  No.  1715.) 


VENTRAL 

VASCULAR 

FOLD 


INTERMEDIATE 
NON-VASCU- 
LAR   FOLD 

DORSAL   VAS- 
CULAR   FOLD 


Fig.  515. — Human  foetus  at  term. 
University  Museum,  No.  1510.) 


Ciecuiu  and  ileo-colic  junction;  ventral  view.     (Columbia 


PLATE    CCLXIV. 


VENTRAL  VAS- 
CULAR   FOLD 


INTCRMEDIATC 
NON-VASCU- 
LAR   FOLD 


Fig.  516. — Human  fcetus  at  term.     Caecum  and  ileo-colic  junction  ;  ventral 
view.     (Columbia  University  Mu.seum,  No.  1548.) 


DORSAL   VAS 
CULAR    FOLD 


INTERMEDIATE 

NON-VASCU 

LAR    FOLD 


Fig.  517. — Adult  human  cacum  and  ileo-colic  junction.    (Columbia  University,  Study 
Collection.) 


CHANGES  IN  THE  POSITION  OF  CMCUM.  241 

schematic  stages  represented  in  Figs.  490  and  491.  The  csecum 
in  this  preparation  has  not  yet  completed  its  rotation  and  still 
turns  its  concavity  upwards  and  to  the  right,  with  the  apex 
imbedded  among  the  terminal  convolutions  of  the  ileum. 

The  ileo-csecal  junction  takes  place  from  right  to  left  in  a  down- 
ward direction.  Nearly  the  entire  mass  of  the  small  intestine  is 
situated  below  and  to  the  left  of  caecum  and  colon,  but  a  terminal 
ileal  coil  still  occupies,  although  evidently  in  the  process  of  with- 
drawal, the  retro-csecal  position,  separating  the  caecum  from  direct 
contact  with  the  dorsal  parietal  peritoneum.  The  withdrawal  of 
this  terminal  coil  of  the  small  intestine  is  accompanied,  or  imme- 
diately followed,  by  a  further  turn  of  the  colon  cephalad  and  to 
the  right,  which  brings  it  into  contact  with  the  caudal  surface  of 
the  liver  and  completes  the  rotation,  producing  a  change  in  the 
relative  positions  of  the  terminal  ileal  coils  and  the  csecum.  In 
the  stages  illustrated  in  Figs.  498  and  499  and  shown  schematic- 
ially  in  Figs.  490  and  491,  the  terminal  coils  of  the  ileum  pass 
from  right  to  left  behind  the  caecum  to  enter  the  colon,  and  the 
concavity  of  the  csecal  pouch  is  directed  upwards  and  to  the  right. 
After  the  final  rotation  has  occurred  (schema.  Fig.  492)  the  ileum 
enters  the  large  intestine  from  the  left  and  from  below,  and  the 
concave  border  of  the  caecum  is  directed  caudad  and  to  the  left. 
This  change  in  relative  position  has  been  accomplished  by  a  revo- 
lution of  the  colon  and  caecum  through  an  arc  of  180°  around  its 
own  long  axis  carrying  the  caecum  above  and  behind  the  small 
intestine  and  bringing  it  into  contact  with  the  dorsal  prerenal 
parietal  peritoneum.  At  the  same  time  the  terminal  coils  of  the 
ileum  turn  downwards  and  to  the  left.  If  this  final  step  in  the 
rotation  of  the  large  intestine  fails  to  occur,  with  otherwise 
normal  development  of  the  parts,  the  ileum  will  persist  in 
entering  the  large  intestine  from  right  to  left  after  the  caecum 
has  obtained  its  final  lodgment  in  the  right  iliac  fossa.  We 
have  had  occasion  to  refer  previously  to  the  significance  of 
these  instances  of  partially  arrested  development  (cf  p.  61,  Figs. 
123,  127  and  128). 

16 


242         MORPHOLOGY  OF  THE  HUMAN  CMGUM  AND  APPENDIX. 

In  Figs.  500  and  501,  taken  from  an  embryo  of  4.9  cm.  vertex- 
coccygeal  measure,  the  final  rotation  of  the  caecum  from  the  posi- 
tion occupied  in  Fig.  498  has  occurred  and  the  concavity  of  the 
pouch  is  directed  caudad  and  towards  the  left.  At  the  same  time 
the  escape  of  the  terminal  ileal  coils  from  behind  the  csecum  and 
beginning  of  the  colon  has  not  yet  taken  place  and  hence  the 
colon  is  still  kept  by  these  coils  from  direct  opposition  to  the 
dorsal  prerenal  parietal  peritoneum.  The  condition  presented  by 
this  preparation  can  be  schematically  indicated  by  Figs.  492  and 
493.  The  rotation  has  carried  the  beginning  of  the  colon  (Fig. 
500),  with  the  csecal  bud  and  appendix  curved  on  itself  and  turn- 
ing its  concavity  to  the  left,  into  the  subhepatic  position.  The 
greater  part  of  the  small  intestinal  coils  lie  now  below  and  to  the 
left  of  the  caecum,  but  the  terminal  ileal  convolutions  (Fig.  500) 
still  occupy  a  retro-csecal  position,  separating  the  pouch  and  the 
colon  from  the  dorsal  parietal  peritoneum.  In  Fig.  501  the  right 
lateral  view  of  the  same  embryo  is  shown  with  the  caecum  and 
colon  depressed  and  turned  to  the  left.  The  termination  of  the 
ileum  reaches  the  ileo-colic  junction  by  passing  behind  the  caecum, 
and  the  immediately  adjacent  ileal  coils  are  still  retro-caecal,  in- 
tervening between  the  pouch  and  the  dorsal  parietal  peritoneum. 

In  the  next  succeeding  stage  (schema,  Fig.  494)  these  coils  of 
the  ileum  turn  downward  and  to  the  left  so  as  to  lie  below  and 
mesad  to  the  caecum  and  colon,  thus  permitting  the  direct  appo- 
sition of  the  large  intestine  to  the  parietal  prerenal  peritoneum. 
The  terminal  ileum  now  passes  from  below  and  to  the  left  up- 
wards and  to  the  right  to  its  junction  with  the  colon.  This  free- 
ing of  the  dorsal  surface  of  caecum  and  colon  from  contact  with 
the  coils  of  the  small  intestines,  and  the  consequent  direct  appo- 
sition of  the  same  to  the  dorsal  parietal  peritoneum  influences  to 
a  great  extent  the  subsequent  arrangement  of  the  parts,  because 
it  affords  the  conditions  necessary  to  the  fixation  of  the  colon  and 
mesocolon  by  adhesion  to  the  parietal  peritoneum  (c£  p.  81). 

Fig.  499,  taken  from  an  embryo  of  6.7  cm.  vertex-coccygeal 
measure,  illustrates  this  stage,  which  is  encountered  in  the  ma- 


CHANGES  IN  THE  POSITION  OF  CJECUM.  243 

jority  of  instances  and  during  which  the  retro-csecal  coils  of  the 
terminal  ileum  are  withdrawn  (schema,  Fig.  493).  The  convo- 
lutions of  the  small  intestine  have  greatly  increased  in  size  and 
number.  The  retro-csecal  ileal  coils,  compared  with  Fig.  500, 
have  shifted  their  position  caudad  and  to  the  left,  so  as  to  he 
below  and  ventrad  of  the  beginning  of  the  colon.  Only  a  single 
coil  remains  behind  the  caecum  and  appendix,  intervening  be- 
tween these  structures  and  the  ventral  surface  of  the  right  kidney, 
and  this  coil  is  in  the  process  of  withdrawal  from  the  dorsal 
position  as  indicated  by  the  superficial  and  short  course  of  the 
coil  which  connects  it  with  the  remaining  ventral  convolutions. 
As  soon  as  the  withdrawal  of  this  single  remaining  dorsal  coil 
is  completed  the  entire  mass  of  the  small  intestines  will  occupy 
a  position  ventrad,  caudad  and  to  the  left  of  the  csecum  and  colon 
(Fig.  494),  which  will  then  rest  directly  against  the  dorsal  parietal 
peritoneum  investing  the  ventral  surface  of  the  right  kidney. 

This  stage  is  illustrated  in  Fig.  502,  taken  from  an  embryo  of 
6.6  cm.  vertex-coccygeal  measure.  The  caecum  and  appendix 
here  occupy  the  subhepatic  position,  well  to  the  right  of  the  me- 
dian line  and  in  the  background  of  the  abdominal  cavity.  The 
terminal  retro-csecal  ileal  coils  of  the  embryo  shown  in  Figs.  500 
and  501  have  descended  caudad  and  to  the  left,  thus  freeing  the 
dorsal  surface  of  caecum  and  colon  and  permitting  direct  contact 
with  the  prerenal  parietal  peritoneum. 

In  the  succeeding  stages  the  caecum  gradually  descends  along 
the  background  of  the  right  lumbar  region  from  the  subhepatic 
position  to  the  right  iliac  fossa,  producing  by  this  descent  the 
ascending  colon  as  a  distinct  segment  of  the  large  intestine. 

It  will  be  observed  that  in  the  stage  shown  in  Fig.  502  (schema, 
Fig.  494)  the  large  intestine  passes  from  the  caecum  to  the  splenic 
flexure  transversely  from  right  to  left  across  the  upper  part  of  the 
abdominal  cavity,  caudad  and  ventrad  of  the  stomach  and  ceph- 
alad  of  the  coils  of  the  small  intestine. 

In  the  following  stages  the  disproportionately  large  size  of  the 
embryonic  liver  compels  the  colon,  as  the  caecum  descends,  to 


244    MORPHOLOGY  OF  THE  HUMAN  CMCUM  AND  APPENDIX. 

assume  an  oblique  position.  When  the  csecal  descent  is  completed 
the  colon  traverses  the  abdominal  cavity  in  contact  with  the 
caudal  surface  of  the  liver  passing  from  the  right  iliac  fossa 
obliquely  cephalad  and  to  the  left  to  the  splenic  flexure  where  it 
becomes  continuous  with  the  descending  colon,  which  segment 
has  early  assumed  its  definite  position  in  the  background  of  the 
abdominal  cavity  on  the  left  side  (Fig.  495).  This  oblique  posi- 
tion of  the  colon  is  seen  in  Figs.  503  and  504.  During  this  stage 
the  increase  in  the  length  of  the  colon  may  lead  to  the  arrange- 
ment seen  in  Fig.  505,  where  the  future  transverse  segment  of  the 
large  intestine  is  bent  caudad  in  form  of  an  arch  whose  summit 
extends  nearly  to  the  pelvis.  This  condition  at  times  persists  in 
the  adult,  in  cases  of  unusually  long  large  intestine,  and  recalls 
the  normal  arrangement  found  in  many  of  the  cynomorphous 
monkeys  in  whom  the  transverse  colon  forms  an  extensive  V-  or 
U-shaped  loop,  with  the  apex  directed  caudad  toward  the  pubic 
symphysis  (Fig.  506).  In  other  instances  in  the  human  foetus 
this  part  of  the  large  intestine  is  thrown  into  a  number  of  shorter 
irregular  coils  (Fig.  507). 

Normally,  however,  in  the  process  of  further  development  and 
with  the  relative  decrease  in  the  size  of  the  liver,  the  hepatic 
flexure  (Fig.  505)  becomes  defined  and  passes  cephalad  and  to 
the  right,  taking  up  the  slack  of  the  bent  segment  and  establish- 
ing the  typical  ascending  and  transverse  colon  as  seen  in  Fig. 
508  (schema.  Fig.  496). 

III.    VARIATIONS   OF   ADULT    C^CUM   AND   APPENDIX. 

The  study  of  the  variations  of  the  adult  caecum  and  appendix 
involves  th6  consideration  of  the  following  points : 

(a)  Shape  of  caecum  and  origin  of  appendix.  {Type  of  adult 
csecum.) 

(b)  Position,  direction  and  peritoneal  relations  of  the  appendix. 

(c)  Arrangement  of  the  vascular  and  serous  ileo-csecal  folds. 
The  peculiarities  encountered  in  any  individual  case  usually 

depend  upon  the  combination  of  all  three  of  these  factors,  which 


SHAPE  OF  CJECUM  AND   ORIGIN  OF  APPENDIX.  245 

together  influence  and  determine  the  arrangement  of  the  struc- 
tures in  the  adult.  Hence  the  examination  of  each  case  should 
be  made  with  reference  to  these  three  points,  which  we  will  now 
consider  in  detail. 

A.    SHAPE   OF   C^CUM   AND    ORIGIN    OF   APPENDIX.    TYPES 
AND  VARIATIONS  OF  ADULT  CiECUM  AND  APPENDIX. 

The  various  forms  of  the  adult  caecum  are  all  derived  by  modi- 
fications from  the  foetal  type  of  the  pouch. 

In  the  embryo  the  csecum  is  funnel-shaped,  narrowing  grad- 
ually and  symmetrically  in  caliber  to  the  root  of  the  appendix, 
at  which  point  the  three  colic  taenia  or  longitudinal  muscular 
bands  of  the  large  intestine  meet.  The  appendix  arises  from  the 
apex  of  the  funnel,  the  lateral  walls  of  which  are  equally  and 
symmetrically  developed.  The  entire  pouch  is  of  a  crescentic 
shape,  the  concavity  of  the  curve  turned  to  the  left  and  directed 
toward  the  caudal  margin  of  the  terminal  ileum.  Two  subdivi- 
sions of  the  foetal  type  are  found : 

I.  The  crescentic  curve  of  the  caecum  is  only  slightly  marked ; 
the  appendix  arises  from  the  most  pendent  part  of  the  pouch  and 
hangs  downward  (schema,  Fig.  509,  /,  a). 

This  form,  which  is  encountered  only  occasionally  in  the  foetus 
and  infant,  is  illustrated  by  the  preparation  shown  in  Fig.  510, 
taken  from  a  foetus  at  term. 

II.  In  the  majority  of  cases  the  inherent  crescentic  shape  of  the 
caecal  pouch  is  pronounced  and  carries  the  termination  of  the 
funnel  with  the  root  of  the  appendix  cephalad  and  to  the  left  to- 
ward the  caudal  margin  of  the  ileo-colic  junction  (schema.  Fig. 
509,  11,  a). 

At  birth  this  typical  arrangement  of  the  caecum  frequently 
places  the  pouch  in  a  nearly  transverse  position,  with  the  apex 
and  the  root  of  the  appendix  turned  to  the  left,  in  contact  with, 
or  under  cover  of  the  terminal  piece  of  the  ileum  at  its  junction 
with  the  large  intestine. 

Figs.  511  and  512  represent  the  parts  in  the  ventral  view  in  the 
foetus  at  term. 


246        MORPHOLOGY  OF  THE  HUMAN  C^CVM  AND  APPENDIX, 

Figs.  513  and  514,  also  taken  from  the  foetus  at  term,  show  the 
caecum  from  the  dorsal  aspect  and  illustrate  well  the  sharp  char- 
acter of  the  curve  which  carries  the  apex  of  the  pouch  up  and  to 
the  left. 

All  the  variations  observed  in  the  adult  caecum  are  derived 
from  these  two  foetal  types  by  a  subsequent  and  usually  asym- 
metrical enlargement  and  dilatation  of  the  pouch. 

We  can  consider  the  derivatives  of  each  form  separately. 

1.  Adult  Caeca  Derived  From  Type  I.  (schema.  Fig.  509,  /"*,  Fig.  510). 
— 1.  Further  development  leads  to  an  enlargement  of  the  caecal 
pouch  and  a  sharper  demarcation  between  the  same  and  the  ap- 
pendix. The  resulting  caecum  is  symmetrical,  with  equally  de- 
veloped lateral  sacculi,  between  which  the  termination  of  the 
longitudinal  muscular  bands  and  the  root  of  the  appendix  is  sit- 
uated (schema.  Fig.  509,  P). 

In  Figs.  515  and  516  two  infantile  caeca  are  shown  which  illus- 
trate this  form.  The  narrow  and  pointed  apex  of  the  foetal  con- 
ical caecum  is  replaced  by  the  capacious  pouch  which  is  differen- 
tiated sharply  from  the  appendix.  Among  the  anthropoid  apes 
the  same  type  is  seen  in  the  caecum  of  the  gibbon  (Figs.  455  and 
456),  and  of  the  young  chimpanzee  shown  in  Fig.  460. 

2.  An  increased  development  of  the  caecal  pouch  in  the  adult 
leads  to  the  protrusion  caudad  of  two  symmetrical  sacculations 
on  each  side  of  the  root  of  the  appendix  which  appears  between 
them.  The  original  apex  of  the  caecal  pouch  is  still  marked  by 
the  implantation  of  the  appendix  and  by  the  termination  of  the 
longitudinal  muscular  bands,  but  the  lowest  level  of  the  pouch  is 
found  on  each  side  of  this  point  at  the  fundus  of  the  secondary 
lateral  sacculi  (schema,  Fig.  509,  P).  Treves,  to  whom  belongs 
the  credit  of  first  accurately  describing  and  classifying  the  forms 
of  the  adult  caecum  based  on  the  development,  found  this  type 
in  three  of  a  series  of  100  cases  examined. 

Figs.  517  and  518  illustrate  this  form  of  the  pouch,  which,  in 
our  experience,  is  frequently  associated  with  the  retro-caecal  erect 


SHAPE  OF  CJECXJM  AND   ORIGIN  OF  APPENDIX.  247 

position  of  the  appendix  (cf.  infra,  p.  251).  Fig.  472  shows  this 
type  in  the  adult  with  pendent  appendix. 

II.  Adult  Caeca  Derived  from  Type  II.  (schema,  Figs.  509-and  511). — 
From  this  more  commonly  observed  type  of  foetal  csecum  the  fol- 
lowing adult  forms  are  developed : 

1.  The  general  shape  and  trend  of  the  foetal  csecum  is  preserved. 
The  pouch  turns  sharply  to  the  left,  carrying  the  apex  with  the 
root  of  the  appendix  upward  toward  the  ileum,  the  appendix 
itself  being  frequently  placed  under  cover  of  the  terminal  coil  of 
the  small  intestine  (schema.  Fig.  509,  IP). 

The  apex  of  the  csecal  pouch  is  either  conical,  narrowing  grad- 
ually toward  the  root  of  the  appendix  (Figs.  520  and  521),  or 
blunt  and  more  sharply  defined  against  the  appendix  (Fig.  522). 
Mr.  Treves  encountered  this  ''persistent  foetal  type"  in  two  per 
cent,  of  his  series. 

The  csecum  is  frequently  sharply  bent  on  itself  in  making  the 
turn  upward  and  to  the  left,  resulting  in  a  deep  indentation  of 
the  concave  border  and  producing  a  corresponding  projecting 
fold  in  the  interior  of  the  pouch  (Fig.  523).  The  ventral  longi- 
tudinal muscular  band  follows  the  crescentic  sweep  of  the  caecum 
to  the  root  of  the  appendix. 

Figs.  524a  and  525&,  representing  the  caecum  of  a  foetus 
at  term  in  the  ventral  and  dorsal  view  respectively,  show  very 
clearly  the  arrangement  of  the  foetal  pouch  from  which  the  adult 
type  with  sharp  angular  bend  is  derived.  This  type  of  adult 
caecum  is  found  in  certain  of  the  anthropoid  apes. 

In  the  orang  (Figs.  458  and  459)  the  caecum  turns  sharply  up- 
ward and  to  the  left,  gradually  narrowing  in  caliber  to  the  root 
of  the  appendix  which  is  coiled  behind  the  termination  of  the 
ileum. 

The  same  type  is  seen  in  Figs.  462  and  463,  taken  from  a  prep- 
aration of  the  adult  chimpanzee.  Fig.  463  shows  especially  well 
the  sharp  bend  between  the  caecum  and  colon  by  means  of  which 
the  apex  of  the  pouch  is  carried  cephalad  behind  the  ileo-colic 
junction. 


248       MORPHOLOGY  OF  THE  HUMAN  CJECUM  AND  APPENDIX. 

Fig.  431,  taken  from  another  specimen  of  the  same  animal, 
shows  the  characteristic  crescentic  curve  of  the  csecum  and  the 
corresponding  course  of  the  longitudinal  muscular  band.  The 
apex  of  the  pouch  in  this  preparation  is  more  rounded  and 
blunt. 

The  same  blunt  termination  of  the  caecum  of  this  type,  with  a 
corresponding  sharper  demarcation  of  the  appendix,  is  seen  in  the 
gorilla  (Fig.  457)  recaUing  the  conditions  found  in  certain  in- 
stances in  the  human  subject  (Fig.  522). 

2.  In  by  far  the  larger  proportion  of  cases  (ninety  per  cent,  in 
Treves'  series)  the  adult  caecum  obtains  its  characteristic  form  by 
an  unequal  development  of  the  walls  of  the  intestine.  The  right 
segment  between  the  ventral  and  dorso-lateral  muscular  bands 
dilates,  forming  a  sacculation  which  projects  caudad  and  consti- 
tutes the  secondary  caput  coli,  while  the  segment  between  the 
lower  border  of  the  ileum  and  the  original  apex,  marked  by  the 
origin  of  the  appendix,  remains  stationary  or  is  further  reduced. 
This  unequal  development  produces  a  relative  displacement  of 
the  root  of  the  appendix  upward  and  to  the  left  toward  the  ileo- 
colic junction. 

In  some  cases  the  primitive  crescentic  curve  of  the  caecum,  as 
indicated  by  the  direction  of  the  ventral  longitudinal  muscular 
band,  is  still  perceptible. 

The  right  wall  of  the  foetal  caecum,  forming  the  most  pendent 
portion  of  the  pouch,  dilates  uniformly  and  thus  constitutes  the 
adult  caput  coli.  The  left  wall  appears  as  a  small  sacculation 
separating  the  root  of  the  appendix  from  the  ileo-colic  junction 
(schema,  Fig.  509,  II,  c).  This  type  of  the  adult  caecum  is  illus- 
trated by  the  preparations  shown  in  Figs.  526-528.  In  other 
cases  part  of  the  right  wall  of  the  caecum  between  the  ventral  and 
dorso-lateral  colic  taenia,  dilates  abruptly  forming  a  very  prom- 
inent rounded  sacculation  which  carries  the  lowest  part  of  the 
pouch  caudad  in  a  sharper  curve  than  in  the  preceding  form  as 
indicated  by  its  deviation  from  the  direction  of  the  longitudinal 
muscular  band  (schema.  Fig.  509,  II,  d). 


PLATE    CCLXV. 


I 


LEFT   OECAL 
SACCULATION 
ROOT   OF 
APPENDIX 

RIGHT   OECAL 
SACCULATION 


Fig.   518. — Adult  human   csecum  and  ileo-colic  junction. 
(Columbia  University  Museum,  No.  234.) 


VENTRAL 

VASCULAR 

FOLD 

BOUNDING 

VENTRAL 

ILEO-CiECAL 

FOSSA 


INTERME- 

ATE   NON- 
VASCULAR 
FOLD 


Fig.  5]  9. — Human  adult  (Smith's  Sound  Eskimo).    Ileo-colic  junction  and  caecum.  (Columbia 
University  Museum,  No.  tSi^O 


> 

X 

a 
o 
o 

w 
h 

<c 
a 
a. 


MS 


0-2 


PLATE    CCLXVII. 


\t 


Fui.  522. 
and  caecum. 


-lluiiiaii  adult  iSiiiith's  Sound  Eskimo).    Ileo-colic  junction 
(Columbia  University  Museum,  No.  ^ffy.) 


SEND    IN 
C>CCAL 
POUCH 
CARRY- 

NG   APEX 
BEHIND 
ILEO-COLIC 
JUNCTION 


Fig.  .523.— Human  adult.    Ileo-colic  junction  and  caecum  ;  dorsal 
view;  dried  preparation.     (Columbia  University  Museum,  No.  200.) 


PLATE    CCLXVIII. 


VENTRAL 

VASCULAR 

FOLD 


Fig.  524.— Human   foetus  at  term.      Ileo-colic  Fig.  525.— Same  preparation  as  Fi.u.  524; 

junction  and  caecum;  ventral  view.    (Columbia  Uni-        dor.sal  view, 
versity  Museum,  No.  1717.) 


ILEUM 


Fig.  526. — Human  adult  (Smith's  Sound  Eskimo).     Ileo-colic  junction  and  caecum  ;   dorsal 
view.     (Columbia  University  Museum,  No.  i|Jt-) 


PLATE    CCLXIX. 


LEFT   C/ECAL 
SACCULATION 


RIGHT   OECAL 
SACCULATION 


E^'S 

^H 

Bl'l 

^ytc.  ^ 

«'^^^^^^^^^^^^H 

^^H 

k' v^ — '''tfl 

fll^^l 

^Hb^^—^x^' ^^^^^^^1 

^^H 

^^^^^^|k^^^^^^^^^^^»^^^^^^^^^^^^^^^H 

^^^1 

ROOT  OF 
APPENDIX 


Fig.  'r21. — Human  adult.     Ileo-colic  junction  and  caecum  ;  ventral  view.     (Columbia  Univer- 
sity, Study  Collection.) 


Fig.  .■ir2rf. — Human  adult.     Ileo-colic  juiicticm  and  caecum;  ventral 
view.     (Columbia  University,  Study  Collection.) 


PLATE    CCLXX. 


RIGHT  OECAL 
SACCULATION 


Fig.  529. — Human  juvenile.     Ileo-colic  junction  and  csecum  ;  dorsal  view. 
(Columbia  University,  Study  Collection.) 


APPENDIX 


ROOT    OF 
APPENDIX 


RIGHT   OECAL 
SACCULATION 


Fig.  530. — Human  adult.    Ileo-colic  junction  and  csecum  ;  dorsal  view.  (Colum- 
bia University  Museum,  No.  115.) 


PLATE    CCLXXI. 


tNTERMEDIATE 

NON-VASCU 

LAR    FOLD 


Fi(i.  .lai. — Human  adult.     Ileo-colic  junction  and  csecuiu  ;  dursal  view. 
University,  Study  Collection.) 


(Colum})ia 


SACCULATION 
REPRESENTING 
APEX   OF  POUCH 

INTERMEDIATE 
NON-VASCU- 
LAR   FOLD 


Fig.  532.— Human  infant.  Ileo-eolic  junction  and 
csecum,  with  secondary  terminal  sacculation.  (Columbia 
University  Museum,  No.  l(j;i-2.j 


PLATE    CCLXXII. 


ROOT   OF 
APPENDIX 


C/ECUM,  DERIVED 
ENTIRELY  FROM 
RIGHT  SACCULA- 
TION 


Fig.  533. — Human  adult.  Ileo-colic  junction  and  csecum  ; 
dorsal  view  ;  dried  preparation.  (Columbia  Uuiversitj-  Mu- 
seum, No.  124.) 


RIGHT 

SACCULATION 

FORMING 

OECAL  POUCH 


ROOT  OF 
APPENDIX 


Fig.  534. — Human  adult,  llco-colif  junction 
and  cfficum  ;  ventral  view ;  dried  preparation. 
(Columbia  University  Museum,  No.  14.) 


SHAPE  OF  GMCUM  AND   ORIGIN  OF  APPENDIX.  249 

Figs.  529-531  afford  examples  of  this  type,  while  Fig.  532, 
taken  from  an  infantile  preparation,  shows  that  the  same  may 
begin  to  develop  at  a  very  early  age.  ^ 

3.  Finally,  in  about  four  per  cent,  to  five  per  cent.,  adult  caeca, 
the  reduction  of  the  wall  to  the  left  of  the  root  of  the  appendix, 
between  this  point  and  the  ileo-colic  junction,  is  complete.  The 
entire  caecal  pouch  is  formed  by  the  dilated  right  wall  between 
the  ventral  and  dorsolateral  muscular  bands.  The  ventral  band 
terminates  at  the  lower  border  of  the  ileo-colic  junction,  from 
which  the  appendix  appears  to  arise,  indicating  the  original  apex 
of  the  foetal  csecum  (schema,  Fig.  509,  11"). 

This  type  is  illustrated  in  the  specimens  shown  in  Figs.  533 
and  534. 

ni.  Adult  Caeca  in  Cases  of  Absence  of  the  Appendix. — A  few  instances 
of  congenital  absence  of  the  appendix  have  been  observed. 

A.  V.  Haller^  describes  the  condition  in  the  following  words : 
''Defuisse  visa  est  in  homine  appendicula,  ut  tuberculum  mini- 
mum superesset." 

Fr.  Arnold,^  without  describing  any  individual  case,  states  that 
"very  rarely  the  appendix  is  entirely  wanting." 

E.  Zuckerkandl,^  reports  having  observed  one  case  of  absence 
of  the  appendix. 

J.  D.  Bryant,"*  reports  a  case  in  which  he  operated  for  appendi- 
citis but  found  "absolutely  no  appendix."  "  The  point  of  tender- 
ness was  found  to  be  a  glandular  growth  located  posterior  to  tha 
usual  site  of  the  appendix." 

Two  instances  of  this  variation  are  shown  in  Figs.  535  and  536, 
taken  from  preparations  in  the  Morphological  Museum  of  Co- 
lumbia University.  In  both  careful  examination  of  the  external 
as  well  as  of  the  mucous  surface  of  the  caecum  demonstrated  the 
entire  absence  of  the  appendix,  and  the  subjects  from  which  they 

1  A.  V.  Haller,  Eletnenta  physiologiae,  Tom.  7,  Liber  24,  Sect.  3. 
*Fr.  Arnold,  Handbuch  der  Anat.  d.  Menschen.     1847.     II.  Bd.,  cloth,  p.  84. 
'E.  Zuckerkandl,  "  Ueber  die  Obliteration  des  Darmfoitsatzes  beim  Menschen."     Anat. 
Hefte  XI.  (Bd.  IV.,  Heftl),  1894,  p.  107. 

*N.  Y.  Med.  Journal,  Vol.  LXIX.,  No,  14,  p.  508. 


250       MORPHOLOGY  OF  THE  HUMAN  CMCUM  AND  APPENDIX. 

were  obtained  presented  no  scars  or  other  evidences  of  operative 
removal  or  of  pathological  processes.  They  are  both,  therefore, 
authentic  instances  of  complete  congenital  absence  of  the  ap- 
pendix, not  of  so-called  retro-peritoneal  or  hidden  appendix.^ 

The  two  examples  differ  from  each  other  in  some  details.  In 
the  first  case  (Fig.  535,  schema.  Fig.  509,  177")  the  caecum  is 
rounded  and  globular.  The  ventral  longitudinal  muscular  band 
is  vertical  and  continued  to  the  lowest  point  of  the  pouch,  which 
greatly  resembles  the  caecum  of  a  typical  cynomorphous  monkey. 

In  the  second  case  (Fig.  536,  schema.  Fig.  509,  IIP)  the  caecum 
turns  upwards  and  to  the  left,  terminating  in  a  sharp  point,  to 
which  several  lobes  of  epiploic  fat  are  attached. 

We  must  assume  that  in  these  cases  the  embryonic  portion  of 
the  caecal  bud  was  developed  just  sufficiently  to  yield  the  re- 
quired adult  pouch  with  nothing  to  spare,  so  to  speak,  which 
could  remain  rudimentary  in  the  form  of  an  appendix. 

Instances  of  exceedingly  rudimentary  and  reduced  appendix 
are  also  encountered. 

In  the  case  illustrated  in  Fig.  537  the  appendix  formed  a  small 
conical  elevation  without  distinct  lumen,  measuring  only  0.5  cm. 
in  length. 

B.  Position  and  Peritoneal  Relations  of  the  Appendix. — Statistical 
records  of  the  position  of  the  appendix  indicate  a  wide  range  of 
variation.  In  general  the  results  obtained  by  different  observers 
show  that  certain  positions  of  the  appendix  are  encountered  in  a 
sufficiently  large  percentage  of  the  cases  to  enable  us  to  adopt  a 
classification,  but  that  a  very  extensive  series  of  records  are  re- 
quired in  order  to  determine  even  approximately  the  prepon- 
derant relations  of  the  appendix.  The  following  are  the  most 
frequently  observed  positions : 

1.  The  appendix  is  directed  upward,  inward  and  to  the  left,  the 
terminal  portion  being  frequently  coiled  under  cover  of  the  ileum 
and  mesentery.  This  position  of  the  appendix  is  largely  due  to 
the  normal  crescentic  curve  of  the  caecum,  which  carries  the  apex 

'Cf.  Quain. 


POSITION  AND  PERITONEAL  RELATIONS  OF  THE  APPENDIX.     251 

of  the  pouch  and  the  root  of  the  appendix  upward  and  to  the 
left.  Its  production  is,  moreover,  favored  by  the  tendency  of 
the  adult  caecum  to  develop  by  dilatation  of  the  ventral  and  right 
wall  at  the  expense  of  the  left  side  of  the  pouch,  thus  relatively 
shortening  the  interval  between  the  origin  of  the  appendix  and 
the  ileo-colic  junction. 

Examples  of  this  commonly  encountered  position  of  the 
appendix  are  given  in  Figs.  512,  513,  514,  520,  521,  523  and 
526. 

2.  The  appendix  is  erected  vertically  behind  the  caecum  and 
ascending  colon  and  closely  attached  to  the  dorsal  wall  of  the 
large  intestine.  In  some  instances  the  caecum  and  colon,  with 
the  adherent  vertical  appendix,  possess  a  free  serous  dorsal  sur- 
face, not  adherent  to  the  parietal  peritoneum  (Figs.  529,  538,  539 
and  540).  In  other  cases  the  ascending  colon  is  fixed  and  the 
greater  part  of  the  retro-colic  appendix  is  buried  in  the  connec- 
tive tissue  which  attaches  the  large  intestine  to  the  abdominal 
parietes  (Fig.  517).  Even  in  these  cases,  however,  the  dorsal  sur- 
face of  the  caecum  and  the  root  of  the  appendix  retain  their  free 
serous  investment. 

3.  The  proximal  part  of  the  appendix  turns  upward  and  to 
the  left  in  continuation  of  the  caecal  curve,  but  the  distal  portion 
is  directed  downward  and  inward,  hanging  over  the  brim  of  the 
pelvis  (Figs.  505,  541  and  542). 

4.  The  appendix  is  directed  downward,  pendent  from  the  lowest 
point  of  the  conical  caecal  pouch,  and  hangs  free  over  the  pelvic 
brim. 

This  type  is  encountered  at  times  in  foetal  and  infantile  sub- 
jects (Figs.  516  and  543). 

5.  The  position  of  the  appendix  is  variant  and  abnormal,  as 
e.  g.  placed  to  the  right  of  caecum  and  colon  (Fig.  544)  or  turned 
up  ventrad  of  the  ileo-colic  junction  (Fig.  545). 

These  variations  in  the  position  of  the  appendix  and  the  result- 
ing peritoneal  relations  of  the  structure  depend  upon  the  follow- 
ing factors. 


252       MORPHOLOGY  OF  THE  HUMAN  CJECUM  AND  APPENDIX. 

1.  The  influence  of  peritoneal  adhesions  estabUshed  during  the 
descent  of  the  caecum  from  the  subhepatic  position  to  the  ihac 
fossa. 

2.  The  inherent  curve  of  the  csecal  pouch. 

3.  The  subsequent  alterations  in  the  caliber  of  the  intestine  and 
the  unequal  development  of  the  pouch  leading  to  the  formation 
of  the  types  of  adult  caeca  above  considered. 

In  determining  the  causes  which  lead  to  the  establishment  of 
any  given  position  of  the  appendix  all  three  of  the  factors  above 
enumerated  must  be  taken  into  account,  although  their  influence 
is  not  exerted  in  every  case  to  an  equal  degree. 

We  have  seen  that  normally,  after  completed  rotation  of  the 
intestine,  the  caecum  with  the  appendix  and  the  beginning  of  the 
colon  are  lodged  in  the  upper  and  right  part  of  the  abdomen, 
below  the  liver  and  in  contact  with  the  prerenal  parietal  peri- 
toneum (schema.  Figs.  493,  502).  During  the  subsequent  stages 
the  caecum  descends  into  the  right  iliac  fossa,  thus  producing  the 
ascending  colon.  It  is  immaterial  whether  this  change  in  position 
is  regarded  as  an  actual  descent  of  the  pouch  over  the  ventral 
surface  of  the  right  kidney,  which  seems  more  probable,  or  as  a 
growing  away  from  the  iliac  region  of  the  remainder  of  the  abdom- 
inal wall,  with  a  concomitant  relative  reduction  in  the  size  of 
the  liver,  producing  a  relatively  lower  position  of  the  caecum, 
or  as  a  combination  of  these  processes.  In  either  case  during  this 
period  the  dorsal  surface  of  the  ascending  colon  and  mesocolon 
normally  becomes  adherent  to  the  dorsal  parietal  peritoneum,  con- 
nective tissue  developing  between  the  opposed  serous  areas  and 
leading  to  the  usual  fixation  of  the  ascending  colon  and  oblitera- 
tion of  the  free  ascending  mesocolon.  If  this  process  of  adhesion 
is  inaugurated  at  an  early  stage,  i.  e.,  before  the  descent  of  the 
caecum  has  been  accomplished,  it  will  act  as  a  drag  on  the  dorsal 
surface  of  the  colic  tube  during  the  subsequent  change  in  position, 
which  carries  the  caecum  downward  into  the  iliac  fossa.  This  leads 
to  a  backward  bend  of  the  caecum  and  appendix  which  parts  will 
in  the  ventral  view  appear  under  cover  of  the  protruding  free 


POSITION  AND  PERITONEAL  RELATIONS  OF  THE  APPENDIX.      253 

ventral  and  lateral  walls  of  the  colon.  Hence  in  many  late 
embryos  and  foetus  at  term  the  lowest  point  of  the  large  intestine 
in  the  right  iliac  fossa  is  formed  by  the  proximal  part  of  the 
csecum  or  by  the  adjacent  segment  of  the  colon,  while  the  original 
termination  of  the  pouch,  with  the  root  of  the  appendix,  is  turned 
backward  and  upward,  and,  as  we  have  seen,  by  reason  of  the 
inherent  shape  of  the  pouch,  also  to  the  left,  carrying  the  begin- 
ning of  the  appendix  frequently  behind  the  terminal  ileum  and 
the  ileo-colic  junction. 

Two  of  the  more  common  positions  of  the  appendix,  viz.,  back- 
wards, upwards  and  inwards  behind  the  ileo-colic  junction,  and 
directly  backward,  erected  vertically  behind  csecum  and  colon, 
can  therefore  in  part  be  referred  to  the  mechanical  conditions  ob- 
taining normally  during  the  descent  of  the  csecum.  Of  course  the 
shape  of  the  csecal  pouch  and  the  later  development  of  the  adult 
type  of  csecum  will  modify  this  influence  in  individual  cases.  We 
have  seen  that  this  early  adhesion  and  the  resulting  effects  on 
the  position  of  caecum  and  appendix  depend  on  the  direct  appo- 
sition of  the  colic  tube  and  mesocolon  to  the  dorsal  parietal  peri- 
toneum. Any  condition  which  will  prevent  or  delay  this  appo- 
sition will  likewise  perpetuate  the  original  embryonal  condition 
of  the  tube,  completely  invested  by  peritoneum  and  with  a  free 
mesocolon. 

Such  an  element  is  found  in  the  persistence  of  the  dorsal  set  of 
ileal  convolutions  in  the  original  retro-csecal  position  beyond  the 
usual  period,  as  indicated  in  the  schematic  Fig.  492,  IV,  a.  If 
the  turn  downward  and  to  the  left  of  these  coils  is  for  any  reason 
delayed  beyond  the  usual  time  the  c£ecal  extremity  of  the  colon 
will  descend  from  the  subhepatic  to  the  iliac  position  without 
coming  directly  into  contact  with  the  dorsal  parietal  peritoneum, 
and  therefore  without  the  usual  peritoneal  adhesion  and  oblitera- 
tion of  the  apposed  serous  surfaces.  The  csecum  under  these  con- 
ditions  descends  without  making  the  backward  bend,  and  the 
origin  of  the  appendix  is  found  at  the  lowest  point  of  the  pen- 
dent funnel-shaped  pouch,  causing  it  finally  to  hang  downward 


254         MORPHOLOGY  OF  THE  HUMAN  C^GUM  AND  APPENDIX. 

or  downward  and  inward  over  the  pelvic  brim.  The  resulting 
form  of  the  csecum  and  the  position  of  the  appendix  is  the  one 
above  described  as  type  la,  lb  and  Ic  (Fig.  509). 

Fig.  510  from  a  foetus  at  term,  and  Figs.  515  and  516  repre- 
senting infantile  caeca,  illustrate  this  form  of  the  pouch,  while  the 
parts  are  shown  in  situ  in  Fig.  543  taken  from  a  preparation  of  a 
five-month  foetus. 

Fig.  546  exhibits  the  condition  obtaining  during  the  develop- 
ment of  this  type  in  the  more  exceptional  instances  of  delayed 
apposition  of  the  colon  to  the  parietal  peritoneum  and  of  in- 
creased development  of  the  terminal  ileal  coils  in  the  original 
retro-csecal  position.  In  this  embryo,  measuring  6.5  cm.  in  vertex- 
coccygeal  length,  the  development  has  progressed  sufficiently  to 
establish  a  distinct  transverse  colon  and  to  bring  the  caecum  and  ap- 
pendix into  the  subhepatic  position.  But  in  place  of  lying  in  con- 
tact with  the  dorsal  parietal  peritoneum,  as  in  the  embryo,  shown  in 
Fig.  502,  over  the  ventral  surface  of  the  right  kidney,  the  increased 
mass  of  the  retro-csecal  ileal  coils  keeps  the  caecum,  already  in 
the  process  of  descent,  in  contact  with  the  ventral  abdominal 
wall.  When  the  final  rotation  of  the  retro-caecal  small  intestinal 
coils  downward  and  to  the  left  occurs,  placing  the  ileo-colic  junc- 
tion (C)  to  the  left  of  the  large  intestine  (schema,  Fig.  494),  the 
ascending  colon  and  caecum  are  not  yet  fixed  by  adhesion  to  the 
dorsal  parietal  peritoneum,  and  the  appendix  will  present  down- 
ward and  to  the  left,  affording  the  necessary  conditions  for  the 
establishment  of  the  permanent  pendent  position  of  the  tube  or 
causing  the  same  to  be  directed  downward  and  inward  over  the 
brim  of  the  pelvis. 

In  contrast  with  the  preceding  is  the  condition  shown  in  Fig. 
547,  taken  from  an  embryo  of  5.9  cm.  vertex-coccygeal  measure. 
The  transverse  colon  in  this  preparation  has  already  begun  to 
assume  an  oblique  position,  passing  down  and  to  the  right  from 
the  splenic  flexure.  The  caecum  and  appendix  are  in  contact 
with  the  dorsal  prerenal  parietal  peritoneum.  The  escape  of  the 
dorsal  set  of  ileal  convolutions  from  the  retro-caecal  position,  by 


I 


POSITION  AND  PERITONEAL  RELATIONS  OF  THE  APPENDIX.     255 

rotation  downwards  and  to  the  left,  is  accomplished.  The  caecum 
and  appendix  are  placed  in  the  position  which  they  would  have 
occupied  in  the  embryo  shown  in  Fig.  546  if  the  dorsal  Jleal  coils 
had  not  prevented,  in  the  latter  preparation,  the  apposition  of  the 
colon  to  the  dorsal  parietal  peritoneum. 

In  considering  the  effect  of  these  variant  conditions  on  the  adult 
arrangement  of  the  structures  it  is  necessary  to  bear  in  mind  the 
second  of  the  above-mentioned  factors,  namely,  the  inherent  shape 
of  the  csecal  pouch  and  appendix  and  the  resulting  direction  of 
its  axis. 

As  previously  stated  the  normal  type  of  the  human  embryonal 
caecum  is  represented  by  the  pouch  of  some  of  the  new-world 
monkeys,  as  Ateles  (Fig.  443)  or  of  certain  lemurs,  of  which  Nycti- 
cebus  (Fig.  420)  furnishes  an  excellent  example.  The  caecum  is 
distinctly  crescentic,  turning  its  concave  margin,  after  completed 
intestinal  rotation,  upwards  and  to  the  left,  toward  the  lower 
margin  of  the  ileum.  The  distal  diminished  segment  of  the 
pouch  in  Ateles  has  already  assumed  the  character  of  a  caecal  ap- 
pendage in  Nycticebus  and  becomes  by  further  reduction  the  typical 
appendix  in  man  and  the  anthropoid  apes,  while  the  proximal 
portion  develops  into  the  capacious  sacculated  caecum  proper. 
Consequently  the  initial  curve  of  the  caecum  tends  to  carry  the 
root  of  the  appendix  upward  and  to  the  left  toward  the  ileo-colic 
3  unction.  This  curve  of  the  pouch,  combined  with  the  mechanical 
effects  produced  by  the  adhesion  of  the  colon  during  the  caecal 
descent,  accounts  for  the  frequency  with  which  the  caecum  in  the 
later  months  of  foetal  life  and  at  birth  is  found  curved  backward, 
upward  and  to  the  left,  placing  the  root  of  the  appendix  under 
cover  of  the  terminal  ileal  convolutions  (Fig.  548).  We  have 
seen  that  this  disposition  of  the  structures  accounts  for  the  pre- 
ponderance of  that  type  of  adult  caecum  which  results  from  the 
further  and  unequal  development  and  dilatation  of  the  segment 
of  the  pouch  situated  to  the  right  of  the  origin  of  the  appendix. 

Bearing  in  mind  the  three  elements  just  considered,  viz.,  the 
effect  of  adhesion  during  the  caecal  descent,  the  inherent  shape 


256       MORPHOLOGY  OF  THE  HUMAN  C^CUM  AND  APPENDIX. 

of  the  pouch  and  the  unequal  alterations  in  caliber  in  the  devel- 
opment of  the  adult  type,  we  can  at  once  take  up  the  resulting 
variations  in  the  peritoneal  relations  of  the  adult  caecum  and 
appendix  which  have  an  important  influence  on  the  progress  of 
pathological  processes  in  this  region.  It  should  be  remembered 
that  in  the  following  schematic  figures  the  colon,  caecum  and  ap- 
pendix are  represented  in  the  profile  view  in  a  straight  line, 
without  indicating  the  characteristic  turn  of  the  crescentic  csecal 
pouch  upwards  and  to  the  left. 

Fig.  549  shows  the  arrangement  in  unimpeded  csecal  descent 
without  adhesion  of  colon  and  mesocolon  to  the  parietal  perito- 
neum. This  disposition  of  the  structures,  if  carried  into  adult 
life,  would  produce  the  permanently  free  ascending  colon  and 
mesocolon  which  we  encountered  exceptionally  in  the  human 
subject  (cf  p.  82)  and  normally  in  certain  of  the  cynomorphous 
monkeys  (p.  83).  The  ascending  colon  and  mesocolon  can, 
under  these  conditions,  be  turned  mesad,  lifting  them  away  from 
the  primary  parietal  peritoneum  investing  the  ventral  surface  of 
the  right  kidney.  Caecum  and  appendix  have,  of  course,  a  com- 
plete serous  investment. 

Normally,  however,  in  the  human  subject,  even  if  the  obliter- 
ation of  the  apposed  serous  surfaces  and  the  resulting  fixation  of 
the  ascending  colon  has  been  delayed  beyond  the  usual  period,  as 
above  indicated,  adhesion  takes  place  subsequently,  involving  the 
dorsal  surface  of  the  ascending  colon  between  the  ileo-colic  junc- 
tion and  the  hepatic  flexure  (schema.  Fig.  550).  The  dorsal  sur- 
face of  the  caecum  usually  retains  its  free  serous  surface  in  whole 
or  in  greater  part.  The  appendix  is  pendent,  entirely  invested 
by  peritoneum  and  hangs  free  in  the  abdominal  cavity,  directed 
toward  the  pelvic  brim,  illustrating  the  effect  of  delayed  fixation 
of  the  colon  on  the  position  of  the  appendix. 

Examples  of  this  condition  are  not  frequent,  and  are  confined 
almost  exclusively  to  foetal  and  juvenile  subjects.  Illustrations 
are  afforded  by  Figs.  515  and  516. 

We  have  already  noted  (p.  246)  the  resulting  foetal  type  of 
pendent  caecum  (Fig.  510). 


PLATE    CCLXXIIL 


DORSAL  VAS- 
CULAR   FOLD 
AND  EPI- 
PLOIC  FAT 


bia  SLSty  S;:s"umrNo!'l07'7.T"""'  '""'""  '°'  '"""  '  ''"°''  °'  'P^'""'"-    (^''^"'"- 


APEX   OF 

CJECUM 

EPIPLOIC 

FAT  MASSES 


Fig.  536.— Human  adult.     Ileocolic  junction  and  csecum,  hardened  in  sHu  ; 
absence  of  appendix.     (Columbia  University  Museum,  No.  715.) 


PLATE   CCLXXIV. 


RUDIMENTARY 
APPENDIX 


Fig.  537.— Human  adult.    Ileo-colic  junction  and  cfecum,  with  rudimentary  appendix.    (Colum- 
bia University  Museum,  No.  1655.) 


Fig.  538.— Human  juvenile.  Ca?cum  in  nitii.  lifted  up  to  sliow  vertical  course  of  appendix, 
situated  behind  cfficum  and  ascending  colon.  The  large  intestine  has  a  free  peritoneal  dorsal 
surface,  and  the  appendix  is  held  in  position  by  adhesion  to  the  large  intestine.  (Columbia  Uni- 
versity, Study  Collection.) 


PLATE    CCLXXV. 


PERITONEUM 
OF   ASCEND 
ING      MESO- 
COLON 


P  OF  AP- 
PENDIX IN 
PERITONEAL 
POCKET 


APPENDIX 


Fig.  539. — Human  adult.     Ileo-colic  junction  and  csecum  ;  dorsal  view.   (Columbia  University- 
Museum,  No.  1594.) 


PLATE    CCLXXVI. 


■ 

■ 

HP" 

^ 

k  ' 

H 

^M 

^B 

'~  'f^Jiit^i 

^^H 

H 

i^^^^B 

^S 

gf^^a 

^il 

■ 

^.     '<ai/^B 

H 

■ 

fl 

1 

ft  '^H 

^41 

^ 

1^1 

APPENDIX 

1 

mf' 

.J^|K 

•  ,.* 

■ 

3 

ILEUM 

1 

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1 

1 

Fig.  540. — Human  adult.    Ileo-colic  junction  and  caecum  ;  dorsal  view.    (Colum- 
bia University  Museum,  No.  1850.) 


Fig.  541. — Human  infant.     Ileo-colic  junction  and  ca»cum ;    ventral   view. 
(Columbia  University,  Study  Collection.) 


PLATE    CCLXXVII. 


LEO-COLIC 
JUNCTION 


.  Fia  542.— Human  infant.  Ilco-colic  junction  and  cfecum;  dorsal 
view.  The  dorsal  surface  of  csecum  as  far  as  root  of  the  appendix  is 
adherent  to  the  parietal  peritoneum  of  the  iliac  fossa.  (Columbia  Uni- 
versity Museum,  No.  394.) 


PLEEN 
STOMACH 


PANCREAS 


TRANSVERSE 
COLON 
GREAT 
OMENTUM 
DESCENDING 

COLON 
DUODENOJEJ- 
UNAL ANGLE 
CUT    MESENTERY 
OFSMALL   INTES- 
TINE 

OMEGA 
LOOP 


an 

bia 


Fig.  543.— Human  foetus  at  fifth  month.  Abdominal  cavity  and  viscera  •  liver 
d  greater  part  of  small  intestine  removed.  (Drawn  from  preparation  in  c'oluni- 
i  University  Museum,  No.  1814.) 


PLATE    CCLXXVIII. 


CiCCUM  AND 
APPENDIX 
NON-ROTA- 
TED 

ILEOCOLIC 
JUNCTION 


UMBILICAL 
VEIN 


GREAT 
OMENTUM 


TERMINAL 
ILEUM 


Fig.  544. — Human  fcetus  at  term.  Abdominal  cavity  and  viscera  ;  greater  part  of 
small  intestine  removed.  (Drawn  from  jn-eparation  iu  Columbia  University  Museum, 
No.  1813.) 


Fig.  545. — Human  fojtus  at  term.     Ileo-colic  junction  and 
csecum.     (Columbia  University  Museum,  No.  998.) 


PLATE    CCLXXIX. 


dorsal (retro 
cjecal)  ileal 

COILS 


INFERIOR 
ILEAL  COILS 


OMEGA 
LOOP 


Fig.  546. —Human  embryo,  6.5  cm.  cervico-coccygeal  measure. 
Abdominal  cavity,  with  liver  removed,  seen  from  "the  right  side. 
(Columbia  University,  Study  Collection.) 


ILEAL  COI  I 


PROXIMAL 
ILEAL  COILS 


Fig.  547. — Human  embryo,  5.9  cm.  vertex-coccygeal  measure.     (Columbia  Uni- 
versity, Study  Collection.) 


PLATE    CCLXXX. 


Fig.  548 — Human  foetus  at  term.  Ileocolic 
junction  and  cpecum.  Pearly  colic  and  cfecal  adhe- 
sion with  retroverted  appendix.  (Columbia  Uni- 
versity Museum,  Study  Collection.) 


¥iG.  549. 


Fig.  550. 


POSITION  AND  PERITONEAL  RELATIONS  OF  THE  APPENDIX.      257 

More  commonly  colic  adhesion  before  the  caecum  obtains  its 
final  iliac  position  results  in  imparting  a  backward  turn  to  the 
pouch,  leading  to  the  peritoneal  disposition  shown  in  schema,  Fig. 
551,  in  which  the  root  of  the  appendix  is  involved  in  the  area 
of  obliteration,  while  the  terminal  segment' remains  free.  An 
example  of  this  condition  is  furnished  by  the  embryo  shown  in 
Fig.  508  (10.7  cm.  vertex-coccygeal  measure).  The  colon  is 
already  segmented  into  an  ascending,  transverse  and  descending 
portion.  The  csecum  is  retroverted  and  its  apex  with  the  ap- 
pendix is  placed  under  cover  of  the  terminal  ileum  which  enters 
the  large  intestine  in  the  direction  from  below  upward  and  to  the 
right.  In  the  side-figure  the  divided  end  of  the  ileum  is  displaced 
upward  to  show  caecum  and  appendix  and  their  relation  to  the 
ileal  mesentery. 

The  disposition  of  the  structures  illustrated  by  this  example 
probably  depends  upon  delayed  adhesion  of  the  colic  embryonal 
tube  to  the  dorsal  parietal  peritoneum.  The  caecum  and  appendix 
appear  to  have  descended  freely  until  the  final  position  in  the 
right  iliac  fossa  has  been  nearly  attained,  adhesion  and  fixation 
of  the  colon  taking  place  just  before  the  descent  is  completed,  and 
thus  producing  the  backward  turn  of  the  caecal  end  of  the  tube. 
Further  development  of  the  caecum  to  form  the  adult  caput  coli 
in  these  cases  leads  to  the  unequal  and  exaggerated  expansion  of 
the  ventral  and  lateral  walls  of  the  pouch,  as  compared  with  the 
fixed  and  adherent  dorsal  wall.  The  former  are  distended  and 
pushed  downwards,  producing  a  relative  recession  of  the  root  of 
the  appendix  upward  and  to  the  left,  until  it  comes  into  relation 
with,  or  even  under  cover  of,  the  ileo-colic  junction  and  of  the 
terminal  ileal  coil  entering  the  colon  at  this  point. 

The  resulting  characteristic  adult  position  of  the  appendix  in 
these  cases  is  as  follows : 

The  termination  of  the  caecum  proper,  and  the  root  of  the 

appendix  are  under  cover  of  the  terminal  ileum  and  frequently 

adherent  to  the  parietal  peritoneum  of  the  iliac  fossa  (Fig.  555). 

The  distal  portion  of  the  appendix  remains  free,  either  hanging 

17 


258       MORPHOLOGY  OF  THE  HUMAN  C^CUM  AND  APPENDIX. 

down  and  in  over  the  brim  of  the  pelvis  (Fig.  542),  or  turned 
upwards  and  to  the  left  and  coiled  in  several  turns  (Figs.  504, 
555  and  556). 

Finally  the  erect  vertical  retro-cxcal  position  of  the  appendix 
presents  several  important  variations  in  the  disposition  of  the 
peritoneal  investment.  In  Fig.  503,  taken  from  an  embryo  of 
7.6  cm.  vertex-coccygeal  length,  the  early  complete  recession  of 
the  retro-csecal  ileal  convolutions  has  probably  permitted  an  early 
apposition  and  adhesion  of  the  beginning  of  the  colon  to  the 
dorsal  prerenal  parietal  peritoneum.  The  subsequent  descent 
into  the  iliac  fossa  produces  a  bend  in  the  ventral  wall  of  the 
colic  tube,  with  a  marked  convexity  directed  downwards  and  for- 
wards, the  apex  of  the  bend  situated  at  or  near  the  level  of  the 
ileo-colic  junction,  while  the  dorsal  colic  wall  is  held  by  the  ad- 
hesion to  the  parietal  peritoneum,  thus  giving  a  backward  incli- 
nation to  the  entire  caecum  and  appendix.  During  the  subse- 
quent descent  of  the  caecum  proper  this  bend  in  the  colon  is 
gradually  diminished  and  the  tube  becomes  straightened  but  the 
apex  of  the  caecum  remains  turned  back  and  the  appendix  is 
placed  in  a  more  or  less  vertical  erect  position  behind  caecum  and 
ascending  colon. 

As  regards  the  disposition  of  the  peritoneal  membrane  in  this 
type  of  appendix  the  following  conditions  are  to  be  noted : 

(a)  (Schema,  Fig.  552.) — The  apex  of  the  caecum  and  the  entire 
appendix  are  extraperitoneal,  imbedded  in  the  loose  connective 
tissue  which  occupies  the  area  of  serous  obliteration.  The  line 
of  peritoneal  reflection  from  the  dorsal  wall  of  the  secondary 
caput  coli  to  the  parietal  peritoneum  of  the  right  iliac  fossa  is 
placed  transversely  below  the  true  apex  of  the  foetal  caecum  and 
the  root  of  the  appendix.  The  latter  tube,  imbedded  in  connec- 
tive tissue,  passes  vertically  upwards  behind  the  ascending  colon, 
its  tip  frequently  reaching  the  ventral  surface  of  the  right  kidney. 
A  well-marked  example  of  this  arrangement  in  the  adult  is 
shown  in  Figs.  557  and  558  (ventral  and  dorsal  view,  with  peri- 
toneal reflection  and  vertical  retrocolic  appendix). 


I 


POSITION  AND  PERITONEAL  RELATIONS  OF  THE  APPENDIX.    259 

(6)  (Schema,  Fig.  553.) — In  other  cases,  with  the  same  position 
of  the  appendix,  the  entire  csecum  and  greater  part  of  the  ascend- 
ing colon  remains  free.  The  vertically  erected  appendix  is  closely 
attached  to  the  dorsal  surface  of  the  ascending  colon,  included 
within  the  serous  investment  of  the  large  intestine.  The  adhesion 
of  the  latter  is  confined  to  a  limited  area  near  the  hepatic  flexure. 
Consequently  caecum  and  greater  part  of  ascending  colon  can  be  • 
turned  up,  away  from  the  parietal  peritoneum  of  the  iliac  fossa, 
and  the  dorsal  surface  of  the  appendix  shows  the  free  serous 
covering  of  the  adjacent  large  intestine. 

We  may  assume  that  this  type  of  the  peritoneal  relations  of  the 
appendix  is  produced  in  one  of  two  ways  : 

1.  Either  the  retro-colic  appendix  has  become  early  attached 
to  the  adjacent  large  intestine,  whose  dorsal  surface  in  large  part 
remains  free,  or 

2.  The  arrangement  of  the  peritoneum  indicated  in  schema. 
Fig.  552,  may  be  subsequently  changed  into  that  shown  in  schema, 
Fig.  553,  by  a  continued  downward  displacement  of  the  csecum, 
producing  a  secondary  serous  investment  of  the  dorsal  surface  of 
appendix  and  part  of  ascending  colon. 

Examples  of  this  type  are  found  both  in  infantile  and  adult 
subjects. 

In  Fig.  538,  taken  from  an  infant  three  years  of  age,  the  caecum  ^ 
is  hfted  up  to  show  the  vertical  position  of  the  appendix  behind 
the  caecum  and  ascending  colon,  the  dorsal  surface  of  the  large 
intestine  retaining  its  free  serous  covering.  Another  illustration 
of  this  arrangement  in  a  juvenile  subject  is  shown  in  Fig.  529. 
The  same  condition  in  the  adult  subject  is  illustrated  in  Figs. 
539  and  540. 

(c)  (Schema,  Fig.  554.) — Occasionally,  with  the  appendix  erected 
vertically  behind  the  ascending  colon,  the  apex  of  the  caecum  and 
the  proximal  portion  of  the  appendix  are  invested  by  peritoneum 
for  a  short  distance  and  the  tip  of  the  appendix  likewise  obtains  a 
free  serous  investment,  while  the  intermediate  greater  portion  of 
the  appendix  and  the  corresponding  segment  of  the  dorsal  surface 


260       MORPHOLOGY  OF  THE  HUMAN  CMCXJM  AND  APPENDIX. 

of  the  ascending  colon  are  extraperitoneal,  adherent  to  the  ab- 
dominal parietes.  Examples  of  this  peritoneal  relation  of  the 
appendix  in  an  infant  are  shown  in  Figs.  559  and  560,  while  Fig. 
509  represents  the  same  arrangement  in  an  adult  specimen.  The 
condition  is  produced  from  the  arrangement  of  schema,  Fig.  554, 
by  secondary  adhesion  and  obliteration  of  the  serous  surfaces 
over  the  intermediate  portion  of  the  retroverted  appendix  and 
the  adjacent  dorsal  surface  of  the  ascending  colon. 

C.   ILEO-C-ffiCAL  FOLDS  AND  FOSS-ffi. 

Certain  peritoneal  folds,  either  mesenteric  in  character,  i.  e., 
containing  blood  vessels,  or  non-vascular,  pass  between  the  ter- 
minal ileum  and  the  caecum  and  appendix,  modifying  in  some 
instances  very  markedly  the  position  and  peritoneal  relations  of 
the  structures. 

In  considering  the  influence  which  these  vascular  mesenteric 
and  non-vascular  serous  folds  exert  in  producing  further  changes 
in  the  shape,  position  and  relations  of  the  human  appendix  it  is 
necessary  to  remember  that  in  the  early  embryonal  stages  these 
bands  and  folds  of  the  peritoneum  appear  only  slightly  marked, 
but  that  they  gain  their  importance  and  influence  on  the  final 
adult  configuration  of  the  csecal  pouch  and  appendix  in  the 
course  of  the  further  development  of  these  structures. 

For  this  reason  the  comparative  study  of  the  corresponding 
parts  in  other  vertebrates,  especially  in  certain  mammalia,  is  of 
the  utmost  value,  if  we  seek  to  explain  and  understand  the  deri- 
vation, significance  and  typical  arrangement  of  these  folds.  We 
have  seen  that  the  caecum  as  found  in  the  large  majority  of 
mammalian  forms  is  equivalent  to  the  caecum  and  appendix  of 
the  human  subject  and  anthropoid  apes  ;  that  in  other  words  the 
vermiform  appendix  represents  the  distal  segment  of  a  caecal 
pouch,  originally  uniform  in  caliber,  which  has  remained  unde- 
veloped, while  the  proximal  portion  has  progressed  evenly  with 
the  general  development  of  the  alimentary  canal  to  form  the 
caecum  proper.     We  have  seen  that  this  tendency  to  retain  the 


ILEO-GMGAL  FOLDS  AND  FOSS^.  261 

distal  portion  of  the  pouch  in  a  rudimentary  condition,  i.  e.,  the 
production  of  an  appendage  to  the  csecum  proper,  is  encountered 
in  several  of  the  lower  forms,  as  certain  Marsupials,  Carnivores, 
Ungulates  and  Lemurs.  The  morphology  of  the  ileo-csecal  folds 
is  hence  best  understood  by  considering  these  structures  as  they 
appear  in  connection  with  the  various  csecal  types  presented  by 
the  lower  mammalia.  Their  arrangement  and  significance  can 
here  be  readily  made  out.  On  the  other  hand,  in  studying  these 
structures  in  the  human  appendix  we  are  following  lines  which 
are  already  becoming  indistinct  on  account  of  the  rudimentary 
character  of  the  organ,  which  we  must  regard  as  undergoing  an 
exceedingly  slow  process  of  reduction,  with  a  view  to  its  ultimate 
elimination  from  the  body.  We  have  seen  that  the  structural 
uncertainty  impressed  on  caecum  and  appendix  by  this  evolution- 
ary influence  finds  its  expression  in  the  wide  range  of  variation 
in  size  and  arrangement  which  these  parts  present.  Necessarily, 
of  course,  this  tendency  to  variation  is  shared,  and  even  exhibited 
to  a  more  marked  degree,  by  what  we  can  term  the  accessory 
structures  connected  with  caecum  and  appendix,  viz.,  the  mesen- 
teric vascular  and  non-vascular  serous  folds  passing  to  them  from 
the  ileum. 

We  can  most  profitably  begin  our  consideration  of  these  folds 
in  a  form  in  which  they  are  preserved  in  their  entire  and  original 
development,  and  then  successively  trace  the  changes  leading  up 
to  the  normal  disposition  in  the  human  subject.  Such  a  type  is 
presented  by  the  caecum  of  Ateles  ater,  the  black-handed  spider 
monkey  (Figs.  444  and  445).  The  caecum  of  this  animal  presents  a 
uniform  crescentic  curve,  with  the  concavity  directed  upward  and 
to  the  left,  and  the  gradual  diminution  in  the  caliber  of  the  pouch, 
from  the  ileo-colic  junction  to  the  apex,  denotes  the  tendency  to 
retain  the  distal  segment  in  a  rudimentary  condition,  foreshad- 
owing the  eventual  formation  of  a  vermiform  appendix. 

In  the  ventral  view,  with  the  terminal  ileum  lifted  up,  the  fol- 
lowing arrangement  of  folds  passing  between  ileum  and  caecum 
is  noted  (Figs.  444  and  445). 


262       MORPHOLOGY  OF  THE  HUMAN  CJECUM  AND  APPENDIX. 

(a)  Vascular  Mesenteric  Folds. — The  peritoneal  vascular  folds, 
carrying  the  blood  vessels  to  supply  the  csecum,  are  two  in  num- 
ber, a  ventral  (1)  and  dorsal  (3).  They  are  of  nearly  equal  size 
and  extent,  passing  from  the  ventral  and  dorsal  aspect  of  the  ileo- 
colic junction  nearly  to  the  apex  of  the  csecum.  Each  contains 
a  branch  of  the  ileo-colic  artery,  which  forks  in  the  ileo-colic 
mesentery,  in  the  angle  between  ileum  and  large  intestine.  The 
ventral  branch  continues  in  the  ventral  mesenteric  fold  (Fig. 
445)  downward  across  the  ventral  surface  of  the  ileo-colic  junc- 
tion to  supply  the  ventral  part  of  the  csecum,  while  the  dorsal 
branch  descends  behind  the  ileo-colic  junction,  preserving  a  simi- 
lar course  in  the  dorsal  mesenteric  fold.  The  dorsal  arterial 
branch  is  somewhat  larger  than  the  ventral  and  its  distribution 
extends  a  little  further  down  to  the  actual  apex  of  the  caecum. 

(b)  Non-vascular  Ileo-csecal  Serous  Reduplication. — Between  the 
two  vascular  mesenteric  folds  a  third  serous  reduplication,  carry- 
ing no  blood  vessels,  is  found  passing  between  the  ileum  and 
caecum.  This  fold  begins,  in  the  preparation  from  which  the 
figure  is  taken,  on  the  ileum  opposite  the  attached  mesenteric 
border,  2.7  cm.  from  the  ileo-colic  junction,  and  passes  for  exactly 
the  same  distance  down  on  the  adjacent  left  concave  surface  of 
the  caecum.  It  is  placed  a  little  nearer  to  the  dorsal  than  to  the 
ventral  vascular  fold,  so  that  it  passes,  if  the  distance  between  the 
two  vascular  folds  on  the  caecum  be  divided  into  three  parts,  at 
the  junction  of  the  dorsal  third  with  the  ventral  two  thirds.  The 
production  of  this  intermediate  non-vascular  ileo-caecal  redupli- 
cation, which  is  of  very  constant  occurrence  in  the  mammalian 
series,  is  to  be  led  back  to  the  development  of  the  caecum. 
When  the  pouch  protrudes  from  the  smooth  surface  of  the  em- 
bryonic intestine  opposite  the  mesenteric  border,  it  extends  back- 
ward along  the  future  small  intestine  and  lifts  off  the  serous  in- 
vestment of  the  gut  in  the  form  of  a  small  peritoneal  plate  filling 
the  interval  between  itself  and  the  adjacent  ileum.  A  very  perfect 
illustration  of  this  process  can  be  seen  in  the  instance  of  Meckel's 
diverticulum  shown  in  Fig.  561.     The  proximal  portion  of  the 


ILEO-CJECAL  FOLDS  AND  FOSSM.  263 

diverticulum  is  here  still  closely  connected  to  the  small  intes- 
tine along  which  it  extends,  both  being  surrounded  by  the 
common  visceral  peritoneum.  The  distal  part  of  the^  diverticu- 
lum has  separated  more  completely  from  the  intestine,  and  in  so 
doing  has  drawn  out  the  serous  investment  in  the  form  of  the 
triangular  fold  which  is  seen  to  pass  between  the  free  margin  of 
the  intestine  and  the  adjacent  surface  of  the  pouch.  The  same 
process  can  be  followed  in  its  different  stages  in  certain  normal 
mammalian  csecal  types. 

In  this  connection  it  may  be  noted  that  the  production  of  the 
csecal  vascular  folds  and  their  relation  to  the  mesentery  is  also 
very  perfectly  illustrated  in  some  forms  of  Meckel's  diverticulum. 
Thus  in  the  preparation  shown  in  Fig.  562,  a  broad  triangular 
serous  fold  passes  from  the  ileal  mesentery  to  the  margin  of  the 
diverticulum,  carrying  the  blood  vessels  which  supply  the  pouch. 
If  the  section  of  the  intestine  to  the  left  of  the  figure  is  regarded 
as  representing  the  terminal  ileum,  that  to  the  right  the  colon, 
and  the  diverticulum  the  csecal  pouch,  the  formation  of  the  fold 
and  its  relation  to  the  mesentery,  blood  vessels  and  intestine  will 
correspond  closely  to  the  ileo-csecal  vascular  folds. 

Fig.  350  shows  the  ileo-colic  junction  and  caecum  of  Halma- 
turus  derbyanus,  the  rock  kangaroo.  The  caecum  here  extends 
backwards  along  the  free  border  of  the  ileum  to  which  it  is  closely 
bound  by  the  common  investing  visceral  peritoneum  for  the 
greater  part  of  its  extent.  In  another  marsupial  form,  a  small 
species  of  opossum  from  Trinidad  (Fig.  349),  the  caecum  has  sep- 
arated itself  more  completely  from  the  adjacent  small  intestine — 
thus  drawing  out  the  peritoneum  into  a  narrow  connecting  fold. 
Finally,  in  the  Virginia  opossum  (Fig.  348),  the  ileum  has  attained 
the  usual  position  at  right  angles  to  caecum  and  colon.  The 
former  pouch  is  separated  from  the  small  intestine  by  a  consider- 
able interval  and  the  angle  between  the  two  is  filled  out  by  a 
well-developed  triangular  serous  fold,  connecting  the  free  mar- 
gin of  the  terminal  ileum  and  the  adjacent  left  border  of  the 
caecum. 


264       MORPHOLOGY  OF  THE  HUMAN  CJECUM  AND  APPENDIX. 

This  is  the  "  intermediate  non-vascular  "  ileo-csecal  fold. 

Passing  now  from  the  condition  presented  by  Ateles,  with  three 
fully  developed  and  distinct  ileo-csecal  folds,  to  the  next  stage 
leading  up  to  the  normal  human  arrangement,  we  find  the  same 
illustrated  in  the  caecum  of  another  new-world  monkey,  Mycetes 
fuscus,  the  brown  howler  monkey,  shown  in  the  ventral  and  dorsal 
views  in  Figs.  449  and  450.  The  ventral  vascular  fold  (Fig.  449, 1) 
is  still  well  developed,  the  contained  ventral  branch  of  the  ileo- 
colic artery  descending  over  the  ventral  wall  of  the  ileo-colic  junc- 
tion and  caecum  and  supplying  both.  The  dorsal  vascular  fold  (Fig. 
450,  2),  on  the  other  hand,  is  nearly  completely  fused  with  the  in- 
termediate non-vascular  reduphcation  (Figs.  449  and  450,  3),  the 
approximation  between  these  structures  exhibited  by  Ateles  having 
in  Mycetes  reached  the  point  of  actual  union,  so  that  the  larger 
dorsal  branch  of  the  ileo-csecal  artery  descends  to  the  apex  of  the 
ca3cum  in  the  following  manner:  The  main  post-csecal  artery 
passes  over  the  dorsal  surface  of  the  ileo-colic  junction  included 
in  a  short  serous  fold  which  corresponds  to  the  dorsal  vascular 
fold  of  Ateles.  Beyond  the  lower  border  of  the  ileo-colic  junction 
this  fold  fuses  with  the  intermediate  n  on- vascular  fold,  one  arte- 
rial branch  descending  along  the  line  of  attachment  of  this  fold 
to  the  caecum,  the  other  distributed  over  the  dorsal  surface  of 
the  pouch. 

A  third  type,  also  taken  from  the  lower  Primates,  is  presented 
by  the  caecum  of  a  cynomorphous  monkey,  Cercopithecus  sahxus, 
the  African  green  monkey,  shown  in  Fig.  432,  in  the  ventral  and 
left  aspect  with  the  terminal  ileum  lifted  up.  The  caecum  of  this 
animal  is  comparatively  short,  somewhat  conical,  terminating  in 
a  blunt  apex.  The  vascular  supply  is  arranged  on  the  same 
type  as  in  Ateles  and  Mycetes,  i.  e.,  a  trunk  of  the  ileo-colic  artery 
divides  at  the  ileo-colic  notch,  one  branch  descending  ventrad,  the 
other  dorsad  of  the  ileo-colic  junction.  The  slightly  larger  size 
of  the  dorsal  vessel,  noted  in  Ateles  and  Mycetes,  has  been 
increased  in  Cercopithecus  until  the  ventral  artery  (1)  supplies 
merely  the  front  of  the  ileo-colic  junction  and  the  upper  part  of 


ILEO-CJSCAL  FOLDS  AND  FOSSM. 


265 


the  adjoining  ventral  wall  of  the  csecum,  while  the  larger  dorsal 
vessel  (2)  descends  behind  the  ileo-colic  junction,  supplying  the 
same  and  the  entire  dorsal  and  apical  portions  of  the  caecum. 
The  relation  of  these  csecal  arteries  to  the  peritoneum  is  moreover 
different  from  that  encountered  in  Ateles.  In  place  of  running  in 
distinct  mesenteric  folds,  as  in  the  latter  species,  the  vessels  pass 
close  to  the  surface  of  the  intestine,  merely  covered  and  partly 
surrounded  by  slightly  redundant  visceral  peritoneum  containing 
numerous  pads  of  epiploic  fat,  which  bead  the  course  of  the  ves- 
sels at  regular  intervals.  Between  the  two  arteries  the  inter- 
mediate non-vascular  fold  (2)  is  seen,  presenting  much  the  same 
arrangement  as  in  Ateles  and  passing  between  the  left  border  of 
the  caecum  and  the  adjacent  margin  of  the  ileum,  nearer  to  the 
dorsal  larger  than  to  the  ventral  smaller  csecal  artery. 

We  have,  therefore,  in  the  three  types  just  considered,  the  fol- 
lowing variations  in  the  arrangement  of  the  vascular  and  non- 
vascular folds : 

1.  (a)  Ventral  and  dorsal  vascular  folds  distinct 

and    free.      Ventral   and   dorsal   csecal 
arteries  of  nearly  equal  size. 
(6)  Intermediate   non-vascular  fold    free    on 
both     surfaces,   placed    nearer   to    the 
dorsal  than  to  the  ventral  vascular  fold. 

2.  (a)  Ventral   vascular   fold   distinct.     Ventral " 

csecal  artery  somewhat  further  reduced 
in  size.  Dorsal  vascular  fold  distinct 
only  over  the  dorsal  surface  of  the  ileo- 
colic junction.  At  the  lower  border  of 
the  ileo-colic  junction  the  dorsal  vascular 
fold  fuses  with  the  intermediate  non- 
vascular fold. 
(6)  Intermediate  non-vascular  fold  free  only 
on  ventral  surface,  the  dorsal  surface 
below  the  ileo-colic  junction  being  fused 
with  the  dorsal  vascular  fold. 


Ateles. 


Mycetes. 


266       MORPHOLOGY  OF  THE  HUMAN  CJECUM  AND  APPENDIX. 


Cercopithecus. 


3.  (a)  Dorsal  and  ventral  vascular  folds  reduced. 
Dorsal  artery  much  larger  than  ventral, 
(fe)  Intermediate  non-vascular  fold  well  devel- 
oped, free  on  both  surfaces. 
We  may  judge  from  this  series  that  the  following  factors  are 
capable  of  materially  modifying  the  definite  arrrangement  of  the 
structures : 

1.  The  vascular  folds  are  capable  of  reduction  until  the  vessels 
run  close  to  the  intestinal  surface,  merely  covered  by  somewhat 
redundant  peritoneum  containing  epiploic  appendages.  ( Cerco- 
pithecus.) 

2.  The  dorsal  caecal  artery  tends  to  assume  in  all  three  forms 
the  greater  share  in  the  csecal  vascular  supply.  This  tendency 
is  slightly  developed  in  Ateles,  becomes  more  pronounced  in  3Iy- 
cetes,  and  is  well  marked  in  Cercopithecus,  in  which  animal  the  dor- 
sal vessel  nearly  replaces  the  ventral  branch,  the  latter  confining 
itself  to  the  ventral  surface  of  the  ileo-colic  junction  and  the  ad- 
jacent ventral  parts  of  the  csecal  wall. 

3.  The  intermediate  non-vascular  fold  is  placed  nearer  to  the 
dorsal  larger  than  to  the  ventral  smaller  csecal  artery.  This  con- 
dition, present  in  both  Ateles  and  Cercopithecus,  foreshadows  the 
fusion  of  the  intermediate  and  dorsal  vascular  folds  at  the  lower 
border  of  the  ileo-colic  junction,  as  seen  in  Mycetes. 

4.  This  fusion  of  the  two  folds  named  in  Mycetes  results  in  giv- 
ing different  values  to  the  dorsal  vascular  fold  in  its  proximal  and 
distal  segments.  The  proximal  segment  descends  from  the  ileo- 
colic notch  behind  the  ileo-colic  junction  to  its  lower  border  as  a 
distinct  fold.  Beyond  this  point  its  fusion  with  the  distal  (csecal) 
segment  of  the  intermediate  fold  rounds  out  a  fossa,  the  inferior 
or  posterior  ileo-csecal,  which  is  consequently  bounded  in  front 
by  the  intermediate  vascular  fold,  behind  by  the  proximal  seg- 
ment of  the  dorsal  vascular  fold,  to  the  right  side  by  the  inner 
wall  of  the  caecum,  between  the  intermediate  and  dorsal  vascular 
folds,  above  by  the  lower  border  of  ileum  and  ileo-colic  junction, 
and  below  by  the  fusion  of  the  two  folds. 


y 


ILEO-CJECAL  FOLDS  AND  FOSSM  267 

This  pocket  or  fossa  which  is  the  most  important  and  constant 
of  the  peritoneal  recesses  in  the  neighborhood  of  the  caecum, 
opens  upward  and  to  the  left.  ^ 

5.  A  superior  or  anterior  ileo-csecal  fossa,  formed  in  cases  of 
well-developed  ventral  vascular  fold  between  the  same  and  the 
ventral  wall  of  the  ileo-colic  junction,  is  of  small  size  and  shallow. 

The  cause  of  the  greater  development  of  the  dorsal  as  com- 
pared with  the  ventral  csecal  artery  is  probably  to  be  sought  in 
the  adhesion  of  the  colon  to  the  dorsal  parietal  peritoneum.  In 
Cercopithecus  the  dorsal  surface  of  the  ascending  colon  is  adherent 
to  the  parietal  peritoneum  down  as  far  as  the  iliac  region  and  be- 
ginning of  the  caecum,  whereas  in  Mycetes  the  entire  caecum,  as 
well  as  the  ascending  colon,  are  free  and  non-adherent  to  the  ab- 
dominal parietes.  The  influence  of  this  adhesion  on  the  arrange- 
ment of  the  vascular  supply  of  the  lower  portion  of  the  ascend- 
ing colon  and  caecum  appears  to  be  important.  Some  of  the 
departures  from  the  Ateles  type  presented  by  Cercopithecus  become 
still  better  developed  in  the  human  subject,  where  the  adhesion 
of  the  ascending  colon  and  the  obliteration  of  the  apposed  serous 
surfaces  of  ascending  mesocolon  and  parietal  peritoneum  is  nor- 
mally complete,  even  if  the  caecum  remains  entirely  free,  or 
only  adheres  to  the  iliac  parietal  peritoneum  in  the  proximal 
part  of  its  dorsal  surface.  Comparison  with  forms  presenting 
non-adherent  colic  and  caecal  tubes  indicates  that  the  adhesion 
determines  the  relative  size  and  arrangement  of  the  ileo-colic 
vessels. 

Thus  the  partially  adherent  colon  and  caecum  of  Cercopithecus 
presents,  compared  with  the  free  tube  of  Ateles  and  Mycetes,  a 
marked  reduction  of  the  ventral  and  a  corresponding  enlargement 
of  the  dorsal  caecal  artery.  Further  progress  in  the  same  direction 
is  noted  in  the  human  subject  where  normally  the  ascending  colon 
and  at  times  the  proximal  portion  of  the  caecum  are  adherent  to 
the  dorsal  parietal  peritoneum. 

It  appears  that  in  the  adhesion  of  the  colic  tube  to  the  parietal 
peritoneum  the  dorsal  ileo-colic  vessels  find  an  element  favorable 


268       MORPHOLOGY  OF  THE  HUMAN  CMCUM  AND  APPENDIX. 

to  their  more  complete  development  and  extension,  replacing  in 
part  or  entirely  the  ventral  csecal  artery  which  becomes  limited 
in  distribution  to  the  region  of  the  ileo-colic  junction.  The  adhe- 
sion and  fixation  of  the  dorsal  wall  of  the  intestine  seems  to  afford 
an  advantage  to  the  dorsal  vessel,  whereas  the  greater  mobility 
and  the  alternating  conditions  of  distension  and  contraction,  with 
variations  of  intracsecal  pressure,  depending  upon  the  contents  of 
the  pouch,  appear  to  operate  unfavorably  upon  the  development 
of  the  ventral  vessel. 

This  view  is  borne  out  by  the  conditions  observed  in  the  excep- 
tional instances  in  which  in  the  human  subject  the  ventral  artery 
assumes  the  large  share  in  the  supply  of  csecum  and  appendix 
(cf.  p.  276).  In  all  the  cases  observed  the  type  of  the  caecum 
indicated  delayed  or  imperfect  colic  adhesion,  and  the  ascending 
mesocolon  remained  partially  free. 

If  we  now  compare  the  conditions  above  described  for  Ateles, 
Mycetes,  Cercopithecus  with  those  usually  found  in  man  and  in  the 
anthropoid  apes,  we  may  appreciate  the  significance  of  the  struc- 
tures encountered  by  beginning  the  investigation  with  a  type  in 
which  the  derivation  of  the  different  parts  is  still  quite  evident. 
Such  a  condition  is  presented  by  the  preparation  shown  in  Fig. 
563,  taken  from  a  child  one  year  of  age.  Here  the  descent  of  the 
caecum  has  evidently  been  quite  rapid  and  uniform  without  dorsal 
adhesion.  The  csecum  and  ascending  colon  remain  free  and  can 
still  be  lifted  away  from  the  ventral  facies  of  the  right  kidney  and 
turned  toward  the  median  line  to  a  point  somewhat  beyond  the 
renal  hilus.  The  caecum  hangs  downward  vertically  and  the 
appendix  arises  from  the  funnel-shaped  apex  of  the  pouch. 

The  ventral  caecal  branch  of  the  ileo-colic  artery  is  sHghtly  de- 
veloped, (1)  as  a  small  vessel  descending  in  an  epiploic  fold  over 
the  ventral  surface  of  the  ileo-colic  junction  as  far  as  the  root  of 
the  appendix.  The  intermediate  non-vascular  fold  (3)  is  well 
marked,  measuring  2.9  cm.  in  length,  extending  from  the  free 
border  of  the  terminal  ileum  to  the  caecum  and  appendix  and 
crossing  over  the  well-developed  dorsal  vascular  fold  (2),  which 


ILEO-CMCAL  FOLDS  AND  FOSSjE.  269 

descends,  as  the  appendicular  mesenterolium,  to  the  tip  of  the 
appendix,  carrying  the  dorsal  artery.  In  studying  the  conditions 
presented  by  this  specimen,  it  is  not  difficult  to  trace  the  analo- 
gous structures  in  the  cseca  of  Cercopithecus,  Ateles  and  Mycetes. 
The  same  vascular  and  non-vascular  serous  reduplications  are 
found  passing  between  the  ileum  and  caecum.  In  accordance 
with  the  type  presented  by  Cercopithecus  the  ventral  artery  is 
much  reduced  and  runs  in  a  short  serous  fold  loaded  with  epi- 
ploic appendages.  The  dorsal  artery,  on  the  other  hand,  is  well 
developed  and  the  intermediate  non-vascular  fold  is  distinct.  In 
their  relative  arrangement  these  folds  follow  the  Ateles  type. 
The  dorsal  vascular  fold  forms  the  true  mesentery  of  the  appen- 
dix, and,  although  close  to  and  crossed  by  the  intermediate  non- 
vascular reduplication,  remains  still  quite  separable  and  distinct 
from  the  same ;  consequently  the  lower  limit  of  the  usual  poste- 
rior ileo-C8ecal  fossa,  produced  by  the  fusion  of  the  dorsal  vascular 
and  the  intermediate  non-vascular  fold,  is  absent. 

A  very  perfect  illustration  of  this  type  of  the  human  ileo-csecal 
fold  is  presented  by  the  preparation  of  Gorilla  savagei  shown  in 
Fig.  457.  The  ventral  fold  and  artery  appear  reduced  in  this 
animal.  The  dorsal  vascular  fold  forms  a  broad  triangular  plate 
of  serous  membrane  carrying  the  dorsal  artery  in  its  free  border 
and  extending  to  the  tip  of  the  appendix. 

The  intermediate  non- vascular  fold  is  narrow  but  distinct,  con- 
tinued for  a  considerable  distance  along  the  ileum,  opposite  to  the 
attached  border,  but  only  for  a  short  extent  along  the  left  border 
of  the  caecum  below  the  ileo-colic  junction.  It  crosses  the  ventral 
surface  of  the  broad  dorsal  vascular  fold  in  passing  to  the  caecum, 
but  remains  entirely  free  and  is  not  adherent  to  the  same. 

Consequently  here  again  the  dorsal  or  posterior  ileo-csecal  fossa 
loses  its  distal  limitation.  The  usual  arrangement  of  the  parts, 
as  found  in  the  human  subject  and  derived  from  the  preceding,  is 
well  illustrated  by  another  anthropoid  ape,  Hylohates  hoolock. 
Fig.  455  shows  the  ileo-caecum  of  this  animal  in  the  ventral  view 
and  the  homologous  parts,  as  compared  with  Gorilla,  are  readily 


270       MORPHOLOGY  OF  THE  HUMAN  CJECUM  AND  APPENDIX. 

recognized.  On  turning  the  terminal  ileum  ventrad  and  cepha- 
lad  (Fig.  456),  it  is,  however,  seen  that  the  intermediate  non-vas- 
cular fold  does  not  merely  cross  the  dorsal  vascular  reduplication, 
as  in  Gorilla,  but  that  it  has  begun  to  adhere  to  the  same  at  the 
point  of  intersection.  Consequently  a  well-marked  and  clearly 
limited  posterior  or  dorsal  ileo-csecal  fossa  is  formed,  bounded 
ventrally  by  the  intermediate  fold  at  its  accession  to  the  csecum, 
dorsally  by  the  proximal  part  of  the  dorsal  vascular  fold,  to  the 
right  by  the  left  wall  of  the  caecum,  behind  by  the  attachment  of 
the  intermediate  fold,  below  by  the  confluence  of  the  two  folds, 
and  above  by  the  lower  border  of  ileum  and  ileo-colic  junction. 

The  open  mouth  of  the  fossa  looks  to  the  left.  Fig.  464,  taken 
from  an  adult  specimen  of  the  chimpanzee.  Troglodytes  niger, 
shows  the  extent  of  the  dorsal  vascular  fold  and  of  its  connection 
with  the  mesentery  of  the  terminal  ileum. 

The  intermediate  non-vascular  fold  extends  from  the  ileum 
downwards  along  the  entire  left  border  of  the  caecum  to  the  root 
of  the  appendix,  fusing  with  the  dorsal  vascular  fold  and  rounding 
out  a  deep  posterior  ileo-csecal  fossa. 

The  typical  arrangement,  as  encountered  in  the  human  subject, 
corresponds  closely  to  the  conditions  presented  by  these  anthro- 
poid apes. 

In  Fig.  564,  taken  from  an  adult  male  human  subject,  the  dorsal 
surface  of  the  ascending  colon  and  of  the  ileo-colic  junction  is 
adherent  to  the  parietal  peritoneum.  The  distention  of  the 
csecum  is  nearly  uniform,  the  right  sacculation  being  only  slightly 
larger  than  the  left.  The  appendix,  measuring  18.4  cm.  in 
length,  arises  from  the  dorsal  surface  of  the  caput  coli,  1.7  cm. 
from  the  point  where  the  ventral  longitudinal  muscular  band 
turns  around  the  caudal  end  of  the  pouch  between  the  two  sac- 
culations, and  3.7  cm.  below  the  caudal  margin  of  the  ileo-colic 
junction. 

The  dorsal  vascular  fold  (2),  forming  the  broad  appendicular 
mesentery  (1),  is  well  developed  and  free  in  its  distal  portion,  ex- 
tending, with  gradually  diminishing  width,  to  the  apex  of  the 


ILEO-CMCAL  FOLDS  AND  FOSSjE.  271 

appendix.  The  proximal  segment  of  this  fold  (between  1  and  2) 
descends  over  the  dorsal  surface  of  the  ileo-colic  junction  and 
meets  (at  4)  the  intermediate  non-vascular  fold  (3)  which  ex- 
tends between  the  ileum  and  csecum,  rounding  out  a  crescentic 
ridge  (4)  which  bounds  the  entrance  into  the  posterior  ileo-csecal 
fossa  (between  2  and  3).  The  influence  of  the  folds  and  of  the 
blood  vessels  on  the  position  and  curves  of  the  appendix  is  quite 
apparent  in  this  preparation. 

The  dorsal  larger  branch  of  the  ileo-colic  artery,  supplying 
cfficum  and  appendix,  passes  over  the  dorsal  surface  of  the  ileo- 
colic junction  (2)  where  the  same,  as  well  as  the  adjacent  dorsal 
surface  of  the  colon,  is  adherent  to  the  parietal  peritoneum.  At 
the  point  where  the  dorsal  vascular  fold  intersects  and  fuses  with 
the  intermediate  non-vascular  fold  (4)  the  artery  divides  into  a 
proximal  and  distal  branch.  The  former  proceeds  to  the  caecum 
and  root  of  the  appendix,  reaching  this  tube  at  the  point  marked 
5.  The  latter  continues  (from  1  on)  in  the  free  border  of  the  ap- 
pendicular mesentery  to  the  beginning  of  the  distal  third  of  the 
appendix,  from  which  point  on  the  fold  extends  as  a  narrow 
reduplication  to  the  tip  of  the  tube.  The  segment  of  the  ap- 
pendix situated  between  these  two  main  arterial  branches  is 
thrown  into  several  coils,  the  expression  of  the  continued  growth 
between  two  points  relatively  fixed  by  the  accession  of  the  two 
arterial  branches.  The  pathological  significance  of  these  bends 
is  apparent  when  we  consider  the  effect  which  the  kinking  of  the 
tube  would  have  on  catarrhal  and  other  inflammations  accom- 
panied by  distension  of  the  appendix. 

Typical  examples  of  the  posterior  ileo-csecal  fossa  and  of  the 
mutual  relationship  of  the  limiting  folds  are  seen  in  Figs.  565  and 
566,  both  taken  from  adult  human  subjects. 

The  significance  and  mutual  relations  of  the  folds  seen  in  the 
preparations  just  considered — which  illustrate  the  typical  adult 
human  arrangement  of  the  structures — will  perhaps  be  best  under- 
stood by  comparison  with  an  adult  ca3cum  in  which  the  infantile 
condition,  as  seen  in  Fig.  563,  has  become  further  developed. 


272  MORPHOLOGY  OF  THE  HUMAN  C^CUM. 

Fig.  567  shows  the  dorsal  view  of  such  a  preparation.  The 
csecum  is  funnel-shaped  with  the  apex,  carrying  the  root  of  the 
appendix,  turned  upward  and  to  the  left,  the  sacculation  to  the 
right  of  the  ventral  muscular  band  being  somewhat  dilated.  The 
appendix — 7.2  cm.  long — turns  sharply  upward  and  to  the  left, 
closely  applied  to  the  left  csecal  sacculation,  passes  dorsad  to  the 
ileo-colic  junction  and  lies  in  its  terminal  part  under  cover  of  the 
ileo-cohc  mesentery.  The  ventral  branch  of  the  ileo-colic  artery 
descends  over  the  ileo-colic  junction,  supplying  the  ventral  wall 
of  the  csecum.  The  intermediate  non-vascular  fold  (3)  is  3.9  cm. 
long  and  entirely  free. 

The  dorsal  vascular  fold  contains  the  large  dorsal  branch  of  the 
ileo-colic  artery,  dividing  into  two  main  branches.  The  first  of 
these  (1)  passes  distally  in  the  free  edge  of  the  fold  to  the  terminal 
part  of  the  appendix.  The  other  proximal  branch  (2)  turns  down- 
ward to  the  root  of  the  appendix  and  the  adjacent  wall  of  the 
caecum,  aiding  materially  in  holding  the  proximal  upturned 
segment  of  the  appendix  in  contact  with  the  left  csecal  sacculation. 

The  intermediate  fold,  short  in  its  csecal  attachment,  does  not 
meet  the  dorsal  vascular  fold  at  any  point,  consequently  the  ileo- 
csecal  fossa  is  not  limited  catidad  toward  the  root  of  the  appendix. 
The  conditions  presented  by  this  specimen  correspond  exactly  to 
those  found  in  the  gorilla  (Fig.  457)  and  in  the  human  infantile 
preparation  (Fig.  563). 

In  comparing  Figs.  564  and  567  it  will  be  noticed  that  the  line 
of  fusion  between  the  intermediate  fold  and  the  dorsal  vascular 
fold  (Fig.  564,  4)  corresponds  to  the  point  where  the  dorsal  ileo- 
csecal  artery  divides  into  its  proximal  and  .distal  branches  (Fig. 
567,  angle  between  1  and  2).  Fig.  567  shows  that  the  proximal 
arterial  twig,  even  without  fusion  with  the  intermediate  fold, 
suffices  to  influence  to  a  considerable  degree  the  curves  and  posi- 
tion of  the  appendix,  inasmuch  as  it  serves  to  hold  the  proximal 
segment  of  the  tube  closely  applied  in  the  erected  position  to  the 
surface  of  the  left  csecal  sacculation.  The  intermediate  segment  of 
the  appendix,  between  the  points  of  accession  of  the  two  arterial 


PLATE    CCLXXXI. 


Fig.  551. 


Fig.  552. 


Fig.  553. 


Fig.  554. 


Fig.s.  549-554.— Schematic  series  illustrating  the  variations  in  the  arrangement  of  the  Cffical 
iiiiu  cone  peritoneum. 


PLATE    CCLXXXII. 


DISTAL 
LIMIT  OF 
PERITONEAL 
ADHESION 


Fig.  555. — Human  foetus  at  term.  Ileocolic  junction  and 
csecum ;  dorsal  view.  The  area  of  peritoneal  adhesion  is  seen 
to  involve  the  dorsal  aspect  of  the  ciecum  as  far  as  the  root 
of  the  appendix.     (Columhia  University  Museum,  No.  1549.) 


^^IB 

■ 

■ 

^M 

H 

COLON 

^^^^H 

H 

H 

^^^P^S 

^^^j^^^^H 

H 

H 

^^H^^ll^H 

p^H 

^H 

^^^E^^^^^^l 

r  ^ 

Hh 

^^hM^^^H 

"•     !-A. 

^^ 

^^^^^^^H 

W^^ 

8Hm 

ii^^^nl 

H^H^^^' 

f'-\yA 

J 

jH 

^B 

I 

^H 

ROOT   OF 
APPENDIX 

^^■■L             ^^^f^^^ 

I 

^1 

LINE  OF, 

i 

^^^^H 

C/ECAL  AD- 

^^^^^^Km^m 

^^^^^1 

HESION   TO 

^^^^^^^^^B 

! 

^^^^^H 

PARIETAL 

^^^^^^^^^A'~~ 

* 

^^^^^1 

PERITO- 

^^^^^^^^^^^L      , 

•i 

^^^^^B 

NEUM 

H^ 

)~>V 

■ 
. 

1 

Fig.  556. — Human  infant.     Ileo  colic  junction  and   caecum,  with  extensive 
adhesion  to  parietal  peritoneum.     (Columbia  Univei-sity  Museum,  No.  301. J 


PLATE    CCLXXXIII. 


PARIETAL 

PERITO 
NCUM   OF 
ILIAC 
FOSSA 


VENTRAL 
VASCULAR 
ILEO-C/E- 
CAL  FOLD 


Fig.  557.— Humau  adult.     Ileo-colic  .junction  and  cfecuin  ;  ventral  view.     (Columbia  Univer- 
sity Museum,  No.  1612.) 


PLATE    CCLXXXIV. 


TIP    OF 

APPENDIX, 

OPENED 


PARIETAL 
PERITONEUM 
OF    ILIAC 
FOSSA      RE- 
FLECTED TO 
THE   RIGHT 
LATERAL 
BORDER    OF 
THE  LARGE 
INTESTINE 


Fra.  538. — Stimc   preiianition   as    Fiji.  T),")? ;    dorsal    view.     The  appondix,  erected  vertically 
between  csecum  and  colon,  is  completely  imbedded  in  connective  tissue. 


TIP  OF 

APPENDIX 

PERITONEAL 


INTERMEDIATE 
NON-PERITONEAL 
SEGMENT    OF 
APPENDIX 

PROXIMAL    POR- 
TION   OF  APPEN- 
DIX  WITH    FREE 
PERITONEAL 
SURFACE 


Fig.  5o9. — Human  infant.  Ileo-colic  junction  and  caecum  ;  dorsal  view.  Retro-colic  apjien- 
dix,  adherent  to  the  free  dorsal  serous  surface  of  the  large  intestine,  with  intermediate  extra- 
peritoneal segment.     (Columbia  University  Museum,  No.  1638.) 


PLATE    CCLXXXV. 


PROXIMAL 
SEGMENT 
OF  APPEN 
DiX,  PERI- 
TONEAL 


TIP  OF  APPEN- 
DIX,  PERITO- 
NEAL 


INTERMEDIATE 
NON-PERITO- 
NEALSEGUENT 
OF  APPENDIX, 
ADHERENT  TO 
THE  PARIETAL 
PERITONEUM 


Fig.  560. — Human  adult.  Ileo-colic  junction  and  ca!fum  ;  dorsal  view.  Appendix  with  inter- 
mediate non-peritoneal  segment,  while  the  proximal  portion  and  the  tip  are  covered  by  serous 
investment.     (Columbia  University  Museum,  No.  KSl.^.) 


PLATE    CCLXXXVI. 


SEROUS  NON- 
VASCULAR FOLD 
BETWEEN 
ILEUM    AND 
DIVERTICULUM 


ROOT   OF 
DIVERTIC- 
ULUM 


OMPHALO- 
MESENTERIC 
ARTERY 


Fig.  561. — Human  adult  ileum  with  Meckel's  diverticulum.    Ileo-diverticular  serous  fold  aud 
persistant  omphalomesenteric  artery.     (Columbia  University  Museum,  No.  1803.) 


PLATE    CCLXXXVII. 


1-    —    -     -     -  ILEUM 


CUT  EDGE 
OF    ILEAL 
MESEN- 
TERY 


VASCULAR 
FOLD,    PRO- 
LONGED 
FROM    ILEAL 
MESENTERY 
CARRYING 
BLOOD-VES- 
SELS TO    DI- 
VERTICULUM 


MECKEL'S 
DIVERTIC- 
ULUM 


Fig.  562. — Human  adult.  Ileum  with  Meckel's  diverticulum,  131.5  cm.  from  ileo-colic 
junction;  a  distinct  vascular  fold  i.s  prolonged  from  the  ileal  mesentery  to  the  margin  of  the 
diverticulum.     (Columbia  University  Museum,  No.  1849.) 


Fig.  563. — Human  ;  child  one  year  old.     Caecum  and  ileo-colic  junction  ;  ventral 
view.     (Columbia  University,  Study  Collection.) 

1.  Ventral  csecal  artery,  surrounded  by  epiploic  appendages. 

2.  Dorsal  vascular  fold,  forming  appendicular  mesentery. 

3.  Intermediate  non-vascular  fold. 


PLATE    CCLXXXVIII. 


Fig.  564. — Human   adult.     Caecum   and  ileocolic  junction.     (Drawn   from  preparation   in 
Columbia  University,  Study  Collection.) 

1.  Dorsal  vascular  fold  at  the  beginning  of  the  distal  free  portion,  forming  the  appendicular 
mesentery. 

2.  Proximal  segment  of  dorsal  vascular  fold,  fusing  with 

3.  Intei'mediate  non-vascular  fold. 

4.  Rounded  edge  of  union  of  dorsal  vascular  and  intermediate  folds  bounding  the  ileo-cfecal 
fossa  caudad. 

5.  Point  of  accession  to  appendix  of  proximal  branch  of  appendicular  artery  derived  from 
posterior  ileo-csecal  artery. 


ILEO-C^GAL  FOLDS  AND  FOSSM.  273 

branches,  is  most  prone  to  develop  spiral  twists  and  bends,  espe- 
cially when  the  usual  fusion  of  the  two  folds  takes  place  and  still 
further  fixes  the  parts,  while  the  distal  segment,  carrying  the 
narrow  crescentic  terminal  appendicular  mesentery,  remains  free. 

Finally,  in  a  certain  number  of  cases,  an  intermediate  condition 
between  the  types  presented  by  Figs.  564  and  567  is  encountered. 
In  Fig.  568  the  general  arrangement  of  the  parts  corresponds 
pretty  accurately  to  that  seen  in  Fig.  566,  but  the  transition  from 
a  completely  free  intermediate  non- vascular  fold  to  one  which  has 
begun  to  fuse  with  the  dorsal  vascular  fold  is  evident.  The 
caecum  is  bent  upward  and  to  the  left,  the  caput  coli  being  formed 
by  the  right  sacculation.  The  appendix,  7.8  cm.  long,  takes  a 
wide  I  -shaped  curve.  The  convexity  of  the  proximal  curve  cor- 
responds to  the  point  where  the  proximal  appendicular  artery  (2) 
passes  to  the  tube.  The  non-vascular  intermediate  fold  (3),  meas- 
uring 2.2  cm.,  fuses  with  the  dorsal  vascular  fold  at  this  point. 

The  three  preparations  illustrate  serially  the  share  which  the 
peritoneal  folds  take  in  the  formation  of  the  posterior  ileo-csecal 
fossa. 

In  Fig.  566  the  failure  of  the  intermediate  fold  to  meet  and 
fuse  with  the  dorsal  vascular  fold  has  left  the  caudal  boundary  of 
the  fossa  (between  2  and  3)  incomplete,  the  ventral  and  dorsal 
walls  being  formed  by  the  folds  in  question.  Fig.  568,  in  which 
fusion  between  the  non-vascular  and  the  dorsal  vascular  folds  has 
commenced,  shows  the  shallow  form  of  the  complete  fossa  under 
these  conditions,  while  in  Fig.  567,  with  extensive  union  of  the 
folds,  the  fossa  has  correspondingly  increased  in  depth. 

A  similar  series  is  shown  in  Figs.  569,  570  and  571.  In  Fig. 
569,  taken  from  an  adult  subject,  the  intermediate  non-vascular 
fold  is  entirely  free,  the  dorsal  branch  of  the  ileo-csBcal  artery 
passes  to  caecum  and  appendix  in  an  area  of  adhesion  between 
parietal  peritoneum  and  the  intestine  which  includes  the  dorsal 
vascular  fold.  There  is  consequently  no  caudal  boundary  to  the 
ileo-csecal  fossa.  Figs.  570  and  571  are  both  taken  from  infantile 
preparations. 

18 


274  MORPHOLOGY  OF  THE  HUMAN  CAECUM. 

In  Fig.  570  the  dorsal  vascular  and  the  intermediate  folds  nearly 
meet  at  the  root  of  the  appendix.  They  serve  to  outline  the 
fossa,  which  appears  completed  in  Fig.  571  by  the  actual  meeting 
and  fusion  of  the  folds. 

The  lleo-cxcal  Folds  in  the  Anthropoid  Apes. — (1)  Chimpanzee, 
Troglodytes  niger. 

The  structures  in  a  juvenile  specimen  of  this  animal  are  shown 
in  Figs.  460  and  461. 

The  ventral  vascular  fold  (Fig.  460,  3),  containing  epiploic  fat, 
descends  over  the  ileo-colic  junction  nearly  to  the  level  of  the 
lower  ileal  margin.  The  intermediate  non-vascular  fold  (Figs. 
460  and  461,  2),  derived  from  the  ileum  opposite  to  the  mesenteric 
border,  passes  to  the  ventral  and  left  aspects  of  the  caecum  and 
meets,  near  the  root  of  the  appendix,  the  dorsal  vascular  fold 
(Fig.  461,  3)  carrying  the  dorsal  csecal  branch  of  the  ileo-colic 
artery,  which  ramifies  over  the  csecum  and  supplies  the  ap- 
pendix. 

The  appendix  measures  12.3  cm.  and  presents  a  terminal  hook, 
slightly  dilated. 

The  appendicular  mesentery  terminates  within  the  concavity  of 
this  hook  and  measures  1.5  cm.  in  width  at  the  broadest  part, 
about  4.5  cm.  from  the  root  of  the  appendix. 

Figs.  462  and  463  show  the  caecum  of  the  adult  chimpanzee  in 
the  ventral  and  dorsal  view.  The  ventral  vascular  fold  (Fig. 
462, 1)  is  well  developed,  heavily  fringed  with  epiploic  appendages. 

The  non-vascular  fold  is  extremely  short  and  tense,  fusing  with 
the  short  appendicular  mesentery  near  the  point  where  in  the 
dorsal  view  (Fig.  463)  the  appendix  is  seen  bent  at  its  origin 
sharply  to  the  right. 

Fig.  464,  also  taken  from  an  adult  specimen  of  the  same  animal, 
shows  a  very  well-developed  dorsal  vascular  fold,  which  fuses  with 
the  intermediate  fold  to  limit  a  distinct  ileo-caecal  recess. 

The  chimpanzee,  therefore,  agrees  closely  with  the  human 
subject  in  the  arrangement  of  the  folds. 

(2)  Orang,  Simia  satyrus. 


ILEO-C^OUM  FOLDS  AND  FOSS^.  275 

In  Figs.  458  and  459  the  arrangement  of  the  folds  in  an  adult 
specimen  of  the  orang  is  shown. 

The  ventral  csecal  artery  (Fig.  458)  is  well  developed,  forming 
with  the  peritoneal  fold  and  epiploic  appendages  surrounding  it^ 
a  sharp  sickle-shaped  edge  which  descends  over  the  ventral  sur- 
face of  the  ileo-colic  junction  following  the  curve  of  the  leftcsecal 
margin,  and  turning  its  concavity  to  the  left  toward  the  entering 
ileum. 

The  ventral  csecal  artery  follows  the  left  margin  of  the  csecum 
below  the  ileo-csecal  junction  and  passes  for  0.5  cm.  upon  the 
portion  of  the  pouch  which  turns  up  behind  the  terminal  ileum. 

The  dorsal  csecal  artery  is  a  vessel  of  large  size,  supplying 
branches  to  the  narrow  appendicular  mesentery  which  extends, 
with  many  epiploic  appendages,  to  within  9  mm.  of  the  blunt 
apex  of  the  appendix.  2.5  cm.  beyond  the  first  bend  in  the  ap- 
pendix the  fold  is  narrowed  to  a  fringe  not  more  than  0.75  cm. 
wide.  Up  to  this  point  the  dorsal  vascular  fold  measures  1.5  cm. 
in  width,  and  just  where  it  narrows  it  is  joined  by  the  intermediate 
non-vascular  fold  (Fig.  459),  which  forms  a  membranous  band,  3.3 
cm.  wide  in  the  middle,  spread  out  in  the  angle  between  the 
lower  and  dorsal  surfaces  of  the  ileum  and  the  dorsal  surface  of 
the  csecum  which  turns  up  behind  the  ileo-colic  junction.  Be- 
tween this  fold  and  the  dorsal  vascular  fold  is  seen  the  deep  recess 
of  the  posterior  ileo-c8ecal  fossa — which  by  reason  of  the  sharp 
curve  of  the  caecum  looks  not  only  to  the  left  but  also  upward 
and  backward. 

Direct  comparison  of  the  preparations  of  these  two  anthropoid 
apes  just  described  with  the  conditions  found  in  many  adult 
human  C8eca  shows  the  close  correspondence  in  the  arrangement 
of  these  folds  and  of  their  influence  on  the  configuration  of  the 
parts. 

Figs.  572  and  573 — taken  from  an  adult  human  subject — show 
a  cfficum  and  appendix  which  almost  reproduces  that  of  the  chim- 
panzee illustrated  in  Figs.  462  and  463  and  closely  resembles  that 
of  the  orang. 


276      MORPHOLOGY  OF  THE  HUMAN  CyECUM  AND  APPENDIX. 

Fig.  572,  giving  the  ventral  view,  shows,  by  the  course  of  the 
ventral  longitudinal  muscular  band,  the  turn  of  the  cfficum  up- 
wards and  to  the  left.  The  ventral  csecal  artery  runs  in  a  fold 
(1)  loaded  with  epiploic  appendages. 

The  non-vascular  intermediate  fold  (Fig.  573,  2)  passes  to  the 
root  of  the  appendix,  joining  the  proximal  segment  of  the  dorsal 
vascular  fold  in  which  the  dorsal  branch  of  the  ileo-colic  artery 
runs  to  the  tip  of  the  appendix.  The  distal  two  thirds  of  the 
appendicular  mesentery  are  free. 

3.  Gibbon,  Hylobates  hoolocJc  (Figs.  455  and  456). — In  the  gibbon 
the  folds  appear  well  developed.  The  intermediate  and  dorsal 
vascular  folds  are  quite  distinct  structures,  although  fusion  (Fig. 
456)  has  begun  at  one  point,  thus  limiting  a  typical  posterior 
ileo-C8ecal  fossa. 

4.  Gorilla,  Gorilla  savagei  (Fig.  457). — Finally  in  the  gorilla  all 
three  folds  appear  quite  distinct  and  separate  from  each  other, 
the  dorsal  vascular  fold  being  especially  well  developed. 

Unusual  and  Aberrant  Types  of  Ileo-csscal  Folds  and  Fossae. — 
{A)  Ventral  csecal  artery  larger  than  the  dorsal,  supplying  the  greater 
part  of  the  caecum  and  the  appendix. 

This  condition  is  occasionally  encountered.  Dr.  Martin,  in  a 
recent  examination  of  the  vascular  supply  of  caecum  and  appen- 
dix in  one  hundred  subjects,  found  it  to  obtain  in  six  instances. 

Apparently  the  dorsal  Avail  of  the  csecum  and  of  the  proximal 
segment  of  the  ascending  colon  remains  free  in  these  cases  and 
does  not  become  adherent  to  the  parietal  peritoneum.  The  shape 
of  the  pouch,  moreover,  indicates  a  free  and  unimpeded  embry- 
onal csecal  descent.  The  normal  relative  size  of  the  two  vascu- 
lar folds  is  reversed,  A  good  example  of  this  variation,  in  the 
caecum  of  an  infant,  is  seen  in  Fig.  516.  The  same  arrangement 
in  an  adult  specimen  is  seen  in  Fig.  574. 

In  the  Slow  Lemur  {Nycticebus  tardigradus)  (Fig.  420)  the  ven- 
tral artery  is  normally  the  larger  of  the  two,  extending  in  the 
ventral  fold  to  the  tip  of  the  reduced  appendix  of  the  caecal  pouch. 

{B)  Fusion  of  ventral  vascular  fold  with  the  intermediate  fold, 


PLATE    CCLXXXIX. 


VENTRAL 

VASCULAR 

FOLD 


ROOT  OF 
APPENDIX 


IN  TERMEDIATE 
NON-VASCU- 
LAR   FOLD 
POST. ILEO- 
CECAL FOSSA 
DORSAL  VAS- 
CULAR   FOLD 


POINT  OF 
UNION    BE- 
TWEEN   DOR- 
SAL VASCU- 
LAR AND  IN- 
TERMEDIATE 
NON-VASCU- 
LAR   FOLDS 


¥ 


Fig.  56.1. — Human  adult.     Ca;cuiii  and  ilco-colic  junction  with  large  intermediate  non-vascu- 
lar fold  and  deep  posterior  ileo-csecal  fos-sa.     (Columbia  University  Museum,  No.  1546.) 


INTERME 
DIATE    NON 
VASCULAR 
FOLD 


ROOT   OF 
APPENDIX 


566. — Human  adult.    Ileo-colic  junction  and  csecum.  (Columbia  University  Museum,  No.  1659.) 


=^        i?       '5 


3  t" 


3      r* 


PLATE    CCXCI. 


Fig.   .".(iB.— Ilinuan   sidult.     Ileo-folic,  juuctiou   and   ciccuin.     (Drawn    from    jjreiiaration   in 
Colunibia  University,  Study  Collection.) 

1.  Distal  and 

2.  Proximal  branch  of  dorsal  iloo-csecal  artery  running  in  dorsal  vascular  fold. 

3.  Intermediate  non-vascular  fold  fusing  witli  2  and  forming  a  narrow  caudal  limit  to  the 
posterior  ileo-etecal  fossa. 


PLATE    CCXCII. 


INTERME- 
DIATE NON- 
VASCULAR 
FOLD 


REFLECTION 
OF  PARIETAL 
PERITONEUM 
TO   LARGE 
INTESTINE 


Fig.  569.- 
No.  1610.) 


-Human  adult.     Ileo-colic  junction  and  c^cum.     (Columbia  University  Museum, 


PLATE    CCXCIir. 


ILEUM 


INTERME- 
)IATE   NON- 
VASCULAR 
FOLD 


DORSAL 
VASCU- 
LAR FOLD 


Fig.  570. — Hiiinaii  infant,  four  days  old. 
(Columbia  University  Museum,  No.  879.) 


Ileo-colic  junction  and  csecum. 


INTERME- 
DIATE NON- 
VASCULAR 
FOLD   FUSING 
WITH    DOR- 
SAL VASCU- 
LAR FOLD  ANI) 
FORMING 
CAUDAL  LIMIT 

OF    ILEO 
CiECAL  FOSSA 


Fia.  571.— Human  infant.     Ileo-colic  junction  and  csecum.     (Columbia 
University,  Study  Collection.) 


PLATE    CCXCIV. 


Fig.   572. — Human   adult,     lleo-cdlic  junction   and 'csecum  ;    ventral    view. 
(Drawn  from  ])rei)aratiou  in  Columbia  University,  Study  Collection.) 
1.  Ventral  vascular  fold. 


Fig.  573. — Dorsiil  view  of  tlie  same  preparation. 

1.  Appendix. 

2.  Intermediate  non-va.scular  fold. 


PLATE  CCXCV. 


VENTRAL 
VASCULAR 
FOLD  CAR- 
RYING MAIN 
OECAL  AND 
APPENDICU- 
LAR ARTERY 


Fig.  574. — Human  adult.     Caecum  and  ileo-colic  junction  ;  well-developed  ventral  vascular 
fold,  carrying  appendicular  artery.     (Columbia  University  Museum,  No.  1613.) 


VENTRAL 

VASCULAR 

FOLD 


Fig.  575. — Human  foetus  at  term.  Ileo  colic  junction  and  csecum ; 
ventral  view.     (Columbia  University  Museum,  No.  1715.) 


PLATE    CCXCVI. 


VENTRAL 

VASCULAR 

FOLD 

ANTERIOR 

ILEO-OECAL 

FOSSA 


FUSION  OF 
INTERME- 
DIATE FOLD 
WITH  VEN- 
TRAL VAS- 
CULAR 
FOLD 


Fig.  576. — Human  adult.     Ileo-colic  junction  and  caecum;  ventral  appendicular  artery  and 
ilep-csecal  fossa.     (Columbia  University  Museum,  No.  1614.) 


PLATE    CCXCVII. 


VENTRAL 

VASCULAR 

FOLD 


POINT    OF 
FUSION 
BETWEEN 
VENTRAL 
VASCULAR 
AND  INTER- 
MEDIATE 
NON-VAS- 
CULAR 
FOLDS 


INTERMEDI- 
ATE   NON- 
VASCULAR 
FOLD 


Fig.  577.— Human  adult.     Ileo-colic  junction  and  caecum  ;  ventral  appendicular  artery 
and  ileo-csecal  fossa.     (Columbia  University  Museum,  No.  1657.) 


PLATE    CCXCVIII. 


VENTRAL 

VASCULAR 

FOLD 


POINT  OF 
FUSION  BE- 
TWEEN VEN- 
TRAL VASCU- 
LAR AND  IN- 
TERMEDIATE 
NON-VASCU- 
LAR   FOLDS 


INTERMEDIATE 
NON-VASCU- 
LAR   FOLD 


Fig.  578. — Human  adult.     Ileo-colic  junction  and  csecum  ;  ventral  appendicular  artery  and 
ileo-csecal  fossa.     (Columbia  University  Museum,  No.  1856.) 


PLATE    CCXCIX. 


VENTRAL 
VASCU- 
LAR  FOLD 

INTERME- 
DIATE  NON- 
VASCULAR 
FOLD 


ROOT   OF 
APPENDIX 


Fig.  579. — Human  adult.     Ilco-colic  junction  and  csecum ;  ventral  appendicular  artery  and 
ileo-csecal  fossa.     (Columbia  University  Museum,  Study  Collection.) 


VENTRAL 

VASCULAR 

FOLD 


INTERMEDI 
ATE  NON- 
VASCULAR 
FOLD 


Fig.  580. — Human  infant.  Ileo-colic  junction  and  caecum  ; 
fusion  of  ventral  and  dor.sal  vascular  folds,  with  intermediate  fold. 
(Columbia  University  Museum,  No.  1663.) 


PLATE   CCC. 


Fig.  5^1. — Human  foetus  at  term.  Ileo-colic 
junction  and  ctecum.  (Columbia  University, 
Study  Collection.) 

1.  Appendix,  terminal  portion  turned  ventrad 
of  ileo-colic  Junction. 

2.  Intermediate  non-vascular  fold. 


Fig.  582. — Human  infant.  Ileo-colic 
junction  and  caecum;  ventral  position  of 
appendix.  (Columbia  University  Museum, 
No.  693.) 


ILEO-C^CAL  FOLDS  AND  FOSSM  217 

resulting  in  the  production  of  a  well-defined  superior  or  ventral  ileo- 
csecal  fossa. 

Normally  the  reduced  ventral  artery  crosses  the-  ileo-colic 
junction  in  a  slightly  developed  ventral  vascular  fold,  closely  ad- 
herent to  the  intestine,  with  a  very  narrow  free  margin.  The  su- 
perior or  ventral  ileo-csecal  fossa  in  these  cases  is  very  shallow  and 
confined  (Fig.  574)  to  the  ventral  surface  of  the  ileo-colic  junction. 
Occasionally  the  fold  is  better  developed  and  fuses  with  the  inter- 
mediate non-vascular  fold,  producing  a  fossa  of  greater  extent, 
which  is  bounded  dorsad  by  the  ileum,  ventrad  and  cephalad  by 
the  ventral  fold,  caudad  by  the  fusion  of  this  fold  with  the  inter- 
mediate reduplication,  and  to  the  right  by  the  left  wall  of  the 
caecum.  Figs.  576,  577,  578  and  579  show  this  aberrant  disposi- 
tion of  the  structures  in  a  series  of  adult  human  caeca. 

A  corresponding  arrangement  is  noted  in  the  preparation  of 
the  caecum  of  Gercopithecus  campbelli  (Fig.  483).  The  large  inter- 
mediate fold  is  joined  by  the  ventral  vascular  fold,  thus  defining 
the  lower  boundary  of  ventral  ileo-caecal  fossa. 

(C)  Union  of  both  vascular  folds  with  the  intermediate  non-vascu- 
lar fold. 

I  have  encountered  one  instance  of  this  arrangement  in  an  in- 
fant, whose  caecum  and  ileo-colic  junction  is  shown  in  Fig.  580. 
Both  the  ventral  and  dorsal  arteries  in  this  case  were  equally 
developed,  and  shared  equally  in  the  supply  of  caecum  and 
appendix.  Both  vascular  folds  fused  with  the  intermediate  fold, 
thus  producing  two  typical  ileo-caecal  fossae,  one  ventral,  the 
other  dorsal. 

(D)  Abnormal  positions  of  the  appendix  due  to  variations  in  the 
arrangement  and  tension  of  the  intermediate  fold. 

Fig.  510  shows  a  foetal  caecum  in  the  ventral  view.  The  ven- 
tral vascular  fold  (3)  is  well  developed.  The  non-vascular  fold 
is  short,  arising  from  the  ventral  surface  of  the  ileum,  instead  of 
from  the  free  border  of  the  intestine  opposite  to  the  mesenteric 
attachment.  It  fuses  with  the  ventral  vascular  fold  a  short  dis- 
tance below  the  ileo-colic  junction,  thus  limiting  a  small  ventral 


278       MORPHOLOGY  OF  THE  HUMAN  CJECUM  AND  APPENDIX. 

ileo-csecal  fossa.  The  dorsal  csecal  artery  in  this  specimen  was 
large,  but  the  fold  carrying  it  extremely  narrow. 

The  preparation  illustrates  the  type  resulting  from  the  reduc- 
tion in  size  and  extent  of  the  non-vascular  and  mesenteric  folds. 
The  intermediate  fold  is  reduced  to  a  short  and  narrow  band. 
Compared  with  the  usual  infantile  type  the  c^Bcum  lacks  the 
characteristic  turn  upwards  and  to  the  left,  possibly  in  conse- 
quence of  the  slight  traction  caused  by  the  rudimentary  inter- 
mediate fold.  The  pouch  occupies  a  nearly  vertical  pendent 
position,  which  the  appendix,  arising  from  the  lowest  point  of  the 
csecal  funnel,  shares.  The  appendix  is  not  drawn  into  the  retro- 
ileal  position  by  the  dorsal  vascular  fold,  which  is  much  reduced. 

In  Fig.  511,  representing  the  caecum  and  appendix  of  a  foetus 
at  term,  the  effect  of  the  tense  non-vascular  intermediate  fold  (2) 
is  seen  in  the  sharp  turn  to  the  left  which  it  imparts  to  the  nearly 
transversely  directed  funnel-shaped  caecum.  The  appendix  (1)  is 
coiled  spirally  for  II  turns  behind  the  ileo-colic  junction,  with 
the  tip  directed  upward  behind  the  mesentery  of  the  terminal 
ileum.  The  non-vascular  intermediate  fold  (2)  extends  to  the 
rest  of  the  appendix.  It  appears  short  in  its  csecal  attachment,  on 
account  of  the  turn  of  the  caecum  backwards  and  to  the  left  and 
the  close  connection  between  the  adjacent  margins  of  the  ileum 
and  caecum. 

In  Fig.  581 — a  foetal  preparation  at  term — the  caecum  is  turned 
to  the  left,  below  and  behind  the  terminal  ileum.  The  non- 
vascular fold  (2)  is  well  developed  as  regards  length  of  ileal  attach- 
ment, but  is  very  narrow  and  tense,  passing  between  ileum  and 
the  proximal  curve  of  the  caecum  behind  the  ileo-colic  junction, 
where  it  merges  with  the  dorsal  vascular  fold.  The  appendix 
takes  a  sudden  turn  caudad  at  this  point  and  then  continues  up 
ventrad  to  the  ileo-colic  junction,  the  proximal  portion  being  kept 
firmly  in  contact  with  the  dorsal  and  caudal  circumference  of  the 
ileum  by  the  tension  of  the  non-vascular  band.  It  is  quite  evi- 
dent that  this  peculiar  turn  oi  the  appendix  is  directly  due  to  the 
confining  influence  of  the  non-vascular  band — which  passes  from 


ILEO-C^CUM  FOLDS  AND  FOSS^.  279 

its  ileal  attachment  almost  directly  dorsad  to  the  point  of  fusion 
with  the  dorsal  vascular  fold,  causing  the  sharp  downward  and 
forward  turn  of  the  proximal  segment  of  the  appendix.  Similar 
cases  with  ventral  position  of  the  appendix  is  shown  in  Figs.  545 
and  582. 


\ 


INDEX. 


ABDOMIMAL  vein  in  Anure  Amphibian, 
158 
in  Reptilia,   167 
in  Iguana,   160 
in  Urodele  Amphibian,  157 
viscera  of  Macacus  rhesus,  77 
Abnormal  positions  of  appendix,  277 
Abomasum,  49 

Accipenser  sturio,  biliary  ducts  in,  145 
pyloric  appendices  in,  120 
ileo-colic  junction  of,  212 
Ailuroidea,  ileo-colic  junction  of,  212 
Alimentary  canal  of  Ammocoetes,  42 
of  Amphioxus,  42 
of  Belone,  40 
of  Chelydra,  58 
of  Cyclostomata,  40,  42 
derivation  of  epithelium,  30 

of  muscular   and   connective 
tissue,  30 
differentiation   from  body-cavity, 

21,  29 
divisions  of,  38 

early  developmental  stages,  21,  29 
mammalian  embryonal  stages,  40 
of  Esox,  40 
of  Echelus  conger,  54 
of  Necturus,  40 
of  Petromyzon,  200 
of  Proteus,  40 
primitive  type,  40,  42 
of  Pseudemys  elegans,  55 
of  Rana,  55 

separation  from  yolk-sac,  22 
tract  of  Necturus  maculatus,  52 
of  Tamandua,  56 
Allantois  in  Amniota,  36 
arteries  of,  63,  146 
derivation  from  alimentary  canal,  35 
function  of,  36 
relation  to  placenta,  36 

to  primitive  intestine,  24 
to  urinary  bladder.  24 
Alligator  mississippiensis,  ileo-colic  junc- 
tion of,  201 
stomach  of,  51 
Ammocoetes,  alimentary  canal  of,  42 

pancreas  in,  117 
Ammodytes.  pvloric  appendix  in,  120 
Amnion,  definition  of,  36 
Amniota,  development  of  liver  in,  143 
Amphibia,  development  of  pancreas,   115 
folds  of  intestine  in,  196 
ileo-colic  junction  of,  201 
Amphibians,  biliary  duets  in,  145 

intestinal  canal  of,  191 
Amphioxus,  alimentary  canal  of,  42 
hepatic  diverticulum  of,  43 
intestinal  canal  of,  191 
Anthropoid  apes,  ileo-caecal  folds  of,  274 


Anthropoidea,  ileo-colic  junction  of,  213 
Anthropomorpha,    ileo-colic    junction    of, 

216 
Anguilla  anguilla,  stomach  of,  47 
Anure  Amphibian,  abdominal  vein  of,  158 
cardiac  vein  in,  158 
musculo-cutaneous  vein  in,  168 
pelvic  vein  in,  158 
post-cava  in,  158 
pre-cava  in,  158 
venous  system  in,  158 
Aorta,      early     condition     of     intestinal 

branches,   32 
Aortal  arterial  system,  development  of,  63 
Aplacentalia,  definition  of,  36 
Appendix,  abnormal  positions  of,  277 
absence  of,  249 
influence  of   dorsal  vascular  fold  on 

shape  of,  271 
origin  of,  and  shape  of  caecum,  245 
position   and   peritoneal   relations  of, 

250 
variations  of  peritoneal  relations,  258 
Arctoidea,  ileo-colic  junction  of,  212 
Arctopithecus  marmoratus,  ileo-colic  junc- 
tion of,  208 
Arctopithecini,   ileo-colic  junction  of,  214 
Arrest    of    development    before    intestinal 

rotation,  60 
Arteries,  of  allantois,  64,  146 
Artery,  caudal,  64 
ileo-colica,  66 
colica  dextra,  66 

media,  66 
coronary,  181 
external  iliac,  64 
gastro-epiploica  sinistra,  108 
hepatic.  65.  179 
ileo-colic,  262 
inferior  mesenteric,  67 
internal  iliac,  64 

pancreatico-duodenalis    inferior,    66 
omphalo-niesenteric,  64,  146 
sacralis  media,  64 
splenic,  65,  108 
superior  mesenteric,  64,  65 
umbilical,  64 
vitelline,  64,  146 
Artiodactyla,    ileo-colic    junction    of,    209 
Arvicola    pennsylvanicus,    ileo-colic    junc- 
tion and  ciccum  of,  211 
Asymmetrical  type  of  ileo-colic  junction, 

223 
Ateles,  ileo-csecal  folds  of,  261 

ater,  ileo-colic  junction  and  csecum  of, 
214 
Atresia  ani,  24,  28 

Axial  mesoderm,  connection  with  splanch- 
nic and  somatic  mesoderm,  22 


281 


282 


INDEX. 


T}AS8ARI8  astuta,  ileo-colic  junction  of, 
JJ       212 

Batrachians,  stomach  of,  44,  46 
Belone,  alimentary  canal  of,  40 
Biliary  ducts  in  Accipenser,  145 
in  Amphibians,  145 
arrangement  of,  145 
in  birds,  145 
in  Buceras,  145 
in  calf,  145 
in  dog,  145 
in  Oaleopithecus,  145 
in  Lophius,  145 
in  Lutra,  145 
■    in  Monotr ernes,  145 
in  Phoca,  145 
in  Reptilia,  145 
in  sheep,  145 
in  Tarsius,  145 
in  Trigla,  145 
in  Xiphias,  145 
Birds,  folds  of  intestine  in,  196 
glandular  stomach  of,.  50 
biliary  duets  in,  145 
ileo-colic  junction  of,  203 
muscular  stomach  of,  50 
venous  system  of,  161 
Blastoderm,  20 
layers  of,  21 
primitive,  20 
Blastodermic  vesicle,  20 
Blastomeres,  20 
Blastula,  20 
Blastosphere,  20 
Body-cavity,  development  of,  21 

primitive  condition  of,  29 
Body-wall,  22 

Boselaphus   tragocamelus,   ileo-colic  junc- 
tion and  caecum  of,  210 
Bos  indicus,  ileo-colic  junction  and  cseeum 
of,  210 
spiral  colon  of,  233 
Bradypus  marmoratus,  ileo-colic  junction 
of,  208 
stomach  of,  51 
Brunner's  glands,  194 
Buceras,  biliary  ducts  in,  145 
Bursa  epiploica  in  lower  forms,  187 

CJECA   of   the   anthropoidea,   compared 
with  the  human,  247 
Caecal  gastric  appendices  of  Dicotyles,  48 
Cseeum  and  appendix,  changes  in  position 
during  development,  239 
development  of,  237 
morphology  of,  237 
variations  of,  244 
descent  of,  76,  243 
of  embryo,  shape  of,  245 
first  appearance  in  human  embryo  of, 

53 
function  of,  219 
non-descent  in  adult,  75 
persistent     subhepatic      position     in 

adult,  75 
in  the  Rodentia,  229 
shape  of,  and  origin  of  appendix,  245 
types  of,  245 
in  the  Ungulata,  229 


Calf,  biliary  ducts  in,  145 
Camel,  gastric  water-cells,  49 
Canal,  medullary,  21,  28 

neuro-enteric,  23 
Cants   familiaris,    ileo-colic   junction   and 

caecum  of,  212 
Capra    cegagrus,    ileocolic    junction    and 

caecum  of,  209 
Cardiac  vein  in  Anure  Amphibian,  158 
Cardinal  veins,  anterior,  147 

posterior,  147 
Carnivora,  gastric  diverticula  of,  48 
ileo-colic  junction  of,  212 
stomach  of,  46,  47 
Carnivorous  birds,  stomach  of,  50 
Casuarius,  duodenum,  biliary  and  pancre- 
atic ducts  of,  115 
intestinal  villi  of,  195 
Castor  fiber,  ileo-colic  junction  and  caecum 
of,  211 
stomach  of,  46 
Cat,  development  of  pancreas,  115 

dorsal  mesogastrium,  spleen  and  pan- 
creas, 126 
lesser  peritoneal  sac,  128 
spleen,  pancreas  and  great  omentum, 
127 
Caudal  artery,  64 

vein  in  Selachian,  154 

in  Urodele  Amphibian,  156 
Caudate  lobe,  170 
Cebidae,  ileo-colic  junction  of,  214 
Cebus  leucophceus,  ileo-colic  junction  and 
caecum  of,  216 
monachus,     ileo-colic     junction     and 
caecum  of,  216 
Cell-body,  19 
Cellulae  coli,   199 

Geratodus,  spiral  intestinal  valve  in,  119 
Cercoleptes  caudivolvolus,  ileo-colic  junc- 
tion of,  212 
Cercopithecus   camphelUi,    ileo-colic   junc- 
tion and  caecum  of,  214 
pogonias,  ileo-colic  junction  and  ci«- 

cum  of,  214 
sahoeus,  ileo-caecal  folds  of,  264 

ileo-colic  junction  and  caecum  of, 
214 
Cervicapra,  intestinal  folds  of,  196 
Cervus  sika,  ileo-colic  junction  and  caecum 
of,  210 
spiral  colon  of,  233 
Cetacea,  ileo-colic  junction  of,  209 
Cetaceans,  stomach  of,  49 
Changes   in   position   during   development 

of  caecum  and  appendix,  239 
Cheek  pouches,  48 

of  Macacus  nemestrinus,  48 
Cheiroptera,  ileo-colic  junction  of,  212 
Chelonians,  liver  of,  144 

stomach  of,  45,  46 
Chelydra,  alimentary  canal  of,  58 
pancreas  of,  ll7 

serpentaria,  ileo-colic  junction  of,  201 
Chick,  development  of  liver  in,  143 

development  of  pancreas  in,  115 
Chlamydophorus,  ileo-colic  jimction  of,  207 
Cholcepus  didactylus,  ileo-colic  junction  of, 
207 


INDEX. 


283 


Chrysothrix    sciureus,    ileo-colic    junction 

and  caecum  of,  214 
Cleft,  urogenital,  27 
Cloaca,  development  of,  24 

division  of,  in  higher  vertebrates,  27 
in  human  embryos,  26 
in  Platypus  anatinus,  26 
structure  of,  in  lower  vertebrates,  25 
in  Iguana  tuherculata,  25 
Cloacal  membrane,  24 

anal  segment,  28 
uro-genital  segment,  28 
Coeliac  axis,  65 

Coelom,    composition    and    derivation    of 
walls,  29 
development  of,  21 
primitive  condition  of,  29 
Colic  bend  of  the  Manidse,  234 
loop  in  Phascolarctos,  234 
Colico-phrenic  ligament,   109 
Colon,  ascending,  adhesions  of,  81 
position  of,  in  foetus,  84 
and  caecum  of  Lagomys  pusillua,  232 
descending,  adhesion  of,  81 

relation  of,  to  left  kidney,  83 
position  as  influenced  by  foetal  liver, 

77 
spiral  coil  of,  233  > 

structural  modifications  of,  230 
Coluber  natrix,  stomach  of,  44 
Common  bile  duct,  145 
Comparative   anatomy   of  hepatic  venous 
circulation,  154 
of  liver,  144 
Comparison    of    human    and    anthropoid 

caeca,  247 
Connective    tissue    and    muscular    fibers, 

derivation  of,  30 
Coprodaeum,  25 
Coronary  artery,  181 

ligaments  of  liver,  173 
Corvus,  caeca  of,  203 
Costo-colic  ligament,  109 
Crocodiles,  stomach  of,  46,  51 
Crop,  48 
Cryptobranchus    alleghaniensis,    ileo-colic 

junction  of,  201 
Cyclostomata,     divisions     of     alimentary 
canal  of,  40,  42 
intestinal  canal  of,  191 
spiral  intestinal  valve  of,  119 
Cyclothurus  didactylus,  ileocolic  junction 

and  caeca  of,  207 
Cyclura  teres,  ileo-colic  junction  and  cae- 
cum of,  202 
Cynocephaltis    anubis,    ileo-colic    junction 
and  caecum  of,  214 
habuin,  ileo-colic  junction  and  caecum 

of,  214 
porcarius,  ileo-colic  junction  and  cse- 

cum  of,  214 
sphinx,  ileo-colic  junction  and  caecum 
of,  214 
Cynoidea,  ileocolic  junction  of,  212 
Cynomorpha,  ileo-colic  junction  of,  213 
Cyprini,  stomach  of,  44 
Cystic  duct,  146 

development  of,  142 
Cysto-enteric  duct,  145 


T\A8YPR0CTA    agouti,   ileo-colic   junc- 
-*-^  tion  and  caecum  of,  211 

spiral  colon  of,  234 
Dasypus  sexcinctus,  ileo-colic  junction  and 

caeca  of,  207 
Dasyurus  viverinus,  ilbo-colic  junction  of, 

206 
Descent  of  caecum,  243 
Derivatives  of  entodermal  intestinal  tube, 

34 
Deuteroplasm,  19 

Development  of  caecum  and  appendix,  237 
of  cystic  duct,  142 
of  gall-bladder,  142 
of  liver,  141 

in  amniota,  143 
in  chick,  143 
in  Elasmobranchs,  143 
in  Teleosts,  143 
of  portal  circulation,  147 
of  spiral  colon,  233 
of  transverse  colon,  244 
of  vascular  system  of  liver,  145 
Dicotyles,  caecal  gastric  appendices  of,  48 
torquatus,  ileo-colic  junction  and  cse- 
cum  of,  209 
Didelphis,  ileo-caecal  folds  of,  263 

virginiana,  ileo-colic  junction  and  cas- 
cum  of,  205 
Digitiform  gland  of  Selachians,  201 
Dipnoeans,  intestinal  canal  of,  191 
spiral  intestinal  valve  in,  119 
Diverticulum  caecum  vitelli  in  birds,  35 
in  Urinator  imber,  35 
Itimme,  35 
vateri,  114 
Dog,  biliary  ducts  in,  145 
Dorsal    mesentery,    early    condition    and 
derivation,  32 
in  lower  vertebrates,  32 
smooth  muscular  fiber  of,  33 
mesogastrium,    area    of    adhesion    to 
parietal  peritoneum,   106 
developmental    changes   in   direc- 
tion and  extent,   103 
definition  of,  100,  101 
gastro-splenic  segment,  108 
redundant  omental  growth,  105 
spleen  and  pancreas  in  cat,  126 
vertebro-splenic  segment,  108 
vascular  ileo-caecal  fold,  262 
fold,  influence  on  shape  of  appendix, 
271 
Double  caecal  pouches  of  birds,  203 
Ducts  of  Cuvier,  147 

in  Selachian,  155 
in  Urodele  amphibian,   156 
omphalo-mesenteric,  22 
of  Santorini,  111 
vitello-intestinal,  22 
of  Wirsung,  111 

development  of,   112 
Ductus  venosus,  149 

changes  after  birth  in,  152 
Duodenal  antrum,  194 
fold  of  cat,  92 

of  Hapale  vulgaris,  93 
inferior,  95 


284 


INDEX. 


Duodenal  fold  of  Nasua  rufa,  92 
superior,  95 
fossae,  92 

superior,  94 

vascular  relations,  95,  96 
loop,  54 
Duodeno-colic  neck,  57 
Duodeno-jejunal  fossa  in  the  cat,  93 
Duodenum,  adhesion  of,  67 
development  of,  53 
peritoneal  relations  of  infra-colic  seg- 
ment, 81 
of  supra-colic  segment,  81 
suspensory  muscle  of,  3.i 
with  biliary  and  pancreatic  ducts,  of 
Casuarius,   115 

TTfCHIDNA    hystrix,    ileo-colic    junction 
-^      and  caecum  of,  204 
Echelus  conger,  alimentary  canal  of,  54 
ileo-colic  junction  of,  200 
intestinal  mucosa  of,  197 
endgut  of,  199 
pyloric  appendix  of,  120 
Ectoderm,  21 
Edentata,  ileo-colic  junction  of,  206 

types  of  ileo-colic  junction  and  csecum 
in,  218 
Egg,  development  of,  20 

structure  of,  19 
Elasmobranchs,   development   of   liver   in, 

143 
Elephas    indicus,    ileo-colic    junction    and 

caecum  of,  210 
Embryonal  intestinal  hernia,  52 
Embryonic  shield,  20 
Embryo,  separation  of,  20 
Endgut  of  Echelus,  199 

extent  and  contained  segments,  38 
function  of,  198 
in  lower  vertebrates,  199 
Enteric  canal,  primitive  condition  of,  29 
Entoderm,  21 

derivatives  of,  28 
Entodermal  intestinal  tube,  derivatives  of, 

34 
Epiblast,  21 
Epiploic  bursa,  107 

early  stages  of,  104 
Epithelium    of   alimentary   canal,   deriva- 
tion of,  30 
Erethizon  dorsatus,  ileo-colic  junction  and 

caecum  of,  211 
Esox,  alimentary  canal  of,  40 
Eunectes  marinus,  ileo-colic  junction  and 

caecum  of,  203 
External  iliac  artery,  63 
perineal  folds,  28 

FCETUS  at  term,  venous  system  of,  162 
Falciform  lisament,  as  part  of  ven- 
tral mesocrastrium,  165 
Felis,  ileo-colic  iunction  and  caecum  of,  212 
leo,  ileo-colic  junction  and  caecum  of, 
212 
Fish,  development  of  pancreas,  115 
folds  of  intestine,  196 
ileo-colic  junction  of.  200 
Fissipedia,  ileo-colic  junction  of,  212 


Fissure,  transverse  anal,  27 
Folds,  ileo-csecal,  260 
Follicles,  solitary,  196 
Foramen  of  Winslow,  174 

boundaries  in  adult  human  sub- 
ject,  184 
caudal  boundary,  178 
in  lower  mammals,  183 
relation  to  duodenal  adhesion,  184 
in  Tamandua  bivittata,  183 
Foregut,  comparative  anatomy  of,  42 
divisions  of,  191 

extent  and  contained  segments,  38 
Formative  yolk,  19 
Fossa  duodeno-jejunalis,  96 
ileo-caecal,  260 
intersigmoidea,  97 
of  Treitz,  92,  96 
Function  of  caecum,  219 

of  pyloric  appendices,  221 
of  pyloric  caeca,  221 
of    spiral    fold    of   intestinal    mucous 
membrane,  220 
Furrow,  primitive  intestinal,  22 

f^ADUS  callarias,  ileo-colic  junction  of, 
vJT      201 

pyloric  appendices  in,  120 
Galeopitheeus,  biliary  ducts  in,  145 

ileo-colic  junction  and  caecum  of,  213 
Gall-bladder,  development  of,  142 

occurrence  of,  144 
Gastric  diverticula  of  Carnivora,  48 
of  Herbivora,  48 
of  Omnivora,  48 
Gastro-hepatic  omentum,  as  part  of  ven- 
tral mesogastrium,  165 
Gastro-splenic  omentum,  109 
Genito-urinary  sinus,  27 

tract,  male,  in  Platypus  anatinua, 
26 
Germinal  area,  20 
membrane,  20 
spot,   19 
vesicle,  19 
Glands  of  Lieberktihn,  194 
Glandular  stomach  of  birds,  50 
Gobius,  stomach  of,  45 
Gorilla  savagei,  ileo-colic  junction  and  cae- 
cum of,  216 
Graafian  follicle,  19 

Greater  curvature,  first  appearance  of,  41 
Groove,  medullary,  21 

primitive  intestinal,  22 

TTALICORE,  ileo-colic  junction  of,  208 
J^     Halmaturus     derbvavus,     ileo-caecal 
folds  of,  263 
ileo-colic    junction    and    cae- 
cum of.  205 
stomach  of.  47 
Hapale    jaccJius,    ileo-colic    junction    and 
cfpcum  of.  214 
vulqaris,  duodenal  fold,  93 
Eeloderma   suspectum,    ileo-colic   junction 

of,  211 
Hepatic  antrum  of  lesser  sac,  170 
arterv.  65 

development  of,  179 


INDEX. 


285 


Hepatic  artery  in  relation  to  foramen  of 
Vvmslovv,  180 
relation  to  duodenal  adhesion,  182 
relation  to  primitive  dorsal  mes- 
entery, IB-A 
cylinders,  143 
ducts,  145 

flexure,  formation  of,  76 
recess  of  lesser  sac,  177 
ridge,  142 
veins,  148 

venous  circulation,  comparative  anat- 
omy ot,  154 
direction  of  current,  152 
summary  of  development,  153 
Hepatic-portal  system  in  Selachian,  155 
in  (jrodele  Amphibian,  157 
vein  in  Iguana,  160 
Hepato-cystic  duct,  145 
Hepato-enteric  duct,  145 
Herbivora,  gastric  diverticula  of,  48 

stomach  of,  46,  47 
Herbivorous  birds,  stomach  of,  50 
Herons,  caecum  of,  204 

stomach  of,  50 
Hippopotamus,  ileo-colic  junction  of,  209 
Human  caeca  compared  with  those  of  the 

Anthropoidea,  247 
Herpestes  griseus,  ileo-colic  junction  and 
caecum  of,  212 
ichneumon,  ileo-colic  junction  and  cse- 
cum  of,  212 
Hycena  striata,  ileo-colic  junction  and  cae- 
cum of,  212 
Hylobates  hoolock,  ileo-colic  junction  and 

caecum  of,  216 
Hypoblast,  21 

Hyracoidea,  ileo-colic  junction  of,  210 
Eyrax  capensis,  ileo-colon,  ileo-caecum  and 
colic  caeca  of,  210 
large  intestine  and  caeca  of,  234 

T GUANA,  abdominal  vein  of,  160 
-*  caecal  pouch  and  valves  of,  202 

hepatic-portal  vein  of,  160 
post-cava  of,  159 
renal-portal  system  of,  159 
sciatic  vein  of,  160 
segmental  veins  of,  161 
tuberculata,    ileo-colic    junction    and 
caecum  of,  201 

cloaca  in,  25 
ventral  mesogastrium  of,  166 
Ileo-caecal  folds,  aberrant  types  of,  276 

of  the  anthropoid  apes,  274 

of  Ateles,  261 

of  Cercopithecus  sabmus,  264 

of  Didelphis,  263 

and  fossae,  260 

of  Halmaturus  derbyanus,  263 

of  Mycetes  fuscus,  264 

smooth  muscular  fibers  of,  33 
fossa,  anterior,  267 

posterior,  271 
fossae,  aberrant  types  of,  276 
Heo-colic  artery,  262 

junction  of  Accipen,ser  sturio,  201 

of  Allipator  missisaippiensin,  201 

of  Amphibia,  201 


Heo-colic  junction  of  the  Arctoidea,  212 
oi  tiie  Ailuroidea,  2i2 
of  Arvicola  pennsylvanicus,  211 
of  the  Anthropoidea,  213 
of  the  Antliropomorpha,  216 
of  the  Artioda^tyJa,  2,0i) 
of  the  Arctopithecini,  214 
of  Arctopithecus  marmoratus,  208 
of  Ateles  ater,  214 
of  Bassaris  astuta,  212 
in  biras,  203 

of  Boselaphus  tragocamelus,  210 
of  Bos  indicus,  210 
in  the  Carnivora,  212 
of  Cards  familiaris,  212 
of  Capra  oegagrus,  209 
in  cases  of  arrested  intestinal  ro- 
tation, 241 
of  Castor  fiber,  211 
of  the  Cebidae,  214 
of  Cebus,  215 

leucophcBus,  216 

monachus,  216 
of  Cercoleptes  caudivolvulus,  212 
of  Cercopithecus  campbellii,  214 

pogonias,  214 

sabcBUs,  214 
of  Cervus  sika,  210 
of  the  Cetacea,  209 
of  Chlamydophorus,  207 
of  Cheiroptera,  212 
of  Chelydra  serpentaria,  201 
of  Choloepus  didactylus,  207 
of  Chrysothrix  sciureus,  214 
of  Corvus,  203 
of  Cryptobranchus  alleghaniensis, 

201 
of  Gyclothurus  didactylus,  207 
of  Cyclura  teres,  202 
of  Cynocephalus,  213 

anubis,  214 

babuin,  214 

porcarius,  214 

sphinx,  214 
of  the  Cynoidea,  212 
of  the  Cynomorpha,  213 
of  Dasyprocta  agouti,  211 
of  Dasypus  sexcinctus,  207 
of  Dasyurus  viverinus,  206 
of  Dicotyles  torquatus,  209 
of  Didelphis  virgtmana,  205 
of  Echelus  conger,  200 
of  Echidna  hystrix,  204 
of  the  Edentata,  206  • 
effect  of  rotation  on  position  of, 

59 
of  Elephas  indicus,  210 
of  Erethizon  dorsatus,  211 
of  Eunectes  marinvs,  203 
of  Felis,  212 

leo,  212 
in  fish,  200 
of  the  Fissipedia,  212 
of  Gadus  callarias,  201 
of  Galeopithecus,  213 
of  Gorilla,  savaqei,  216 
of  Halicore,  208 
of  Halmaturus  derbyanus,  205 
of  Hapale  jacchus,  214 


286 


INDEX. 


Ileo-colic   junction   of   Ueloderma   suspec- 
turn,  204 
of  the  herons,  204 
of  Herpestes  icUneumon,  212 
of  Hippopotamus,  209 
of  Hycena  striata,  212 
of  Hylobates  hoolocfc,  216 
of  Hyracoidea,  210 
of  Uyrax  capensis,  210 
of  Iguana  tuberculata,  202 
of  the  Insectivora,  213 
of  Lagothrix  humboldtii,  216 
of  Lamellirostra,  203 
of  Lemur  macaco,  213 

mongoz,  213 
of  the  Lemuroidea,  213 
of  Lepus  cuniculus,  211 
of  Macacus,  214 

cynomolgus,  214 

ochreatus,  214 

pileatus,  214 

rhesus,  214 
of  mammalia,  204 
of  Manatus  americanus,  208 
of  Manis  longicauda,  208 
of  Marsupialia,  204 
of  Monotremata,  204 
of  Midas  geoffrei,  214 

ursulus,  214 
of  Monodon,  209 
of  Mustela,  212 
of  Mycetes  cahaya,  214 

fuscus,  215 
of  Myoxus,  211,  212 
of  Myrmecophaga  juhata,  207 
of  liasua  rufa,  212 
of  Necturus  maculatus,  201 
non-vascular  serous  folds,  262 
of  Nycticehus  tardigradus,  213 
of  Nyctipithecus  commersonii,2l4: 
of  Ornithorhynchus  anutinus,  204 
of  Orycteropus,  208 
of  Orj/a;  leucoryx,  210 
of  Otolicnus  crassicaudatus,  273 
of  Paradoxurus  typus,  212 
of  Perameles  nasuta,  206 
of  the  Perissodactyla,  210 
of  Phascolarctos  cinereus,  205 
of  Phascolomys  wombat,  206 
of  Phocwna,  209 
of  Phoca  vitulina,  212 
of  Physeter,  209 
of  the  Pinnipedia,  212 
of  the  piscivorous  divers,  203 
of  Pithecia  satanas,  215 
of  Pleuronectes  maculatus,  201 
of  the  Primates,  213 
of  the  Proboscidea,  210 
of  Proteles  lalandii,  212 
of  Pseudemys  elegans,  201 
of  Pteropus  medius,  212 
of  Rana  catesbiana,  201 
of  the  Ratitae,  203 
of  Reptilia,  201 
of  the  Rodentia,  211 
serial  review  in  Vertebrata,  200 
of  the  Sirenia,  208 
of  Simia  satyrus,  216 
of  atrix,  203 


Ileo-colic  junction  of  Struthio  africanus, 
204 
of  8us  scrofa,  209 
asymmetrical  type,   223 
symmetrical  type,  221 
of  Tamandua  bivittata,  208 
of  Tapirus  americanus,  210 
of  Tarsius  spectrum,  213 
of  Tatusia  novemcincta,  207 
of  Taxidea  americana,  212 
of  Tolypeutes,  207 
of  Trichosurus  vulpinus,  205 
of  Troglodytes  niger,  217 
types  of,  and  crecum,  217 
in  Edentata,  218 
in  Marsupialia,  218 
of  Vrsus,  212 
of  the  Ungulata,  209 
of  Vulpes  fulvus,  212 
vascular  mesenteric  folds  of,  262 
of  Xenurus,  207 
of  Zalophus  gillespiei,  212 
Iliac  vein  in  Urodele  Amphibian,  157 
Inferior  mesenteric  artery,  67 
Infracolic   compartment,   secondary   parie- 
tal peritoneum  of,  85,  86 
Insectivora,  ileo-colic  junction  of,  213 
Intermediate  duodenal  fold,  96 

non-vascular  ileo-caecal  fold,  262 
Internal  iliac  artery,  63 

perineal  folds,  27 
Intestinal  blood  vessels,  effect  of  intestinal 
rotation  on,  59 
canal  of  Amphioxus,  191 
of  Amphibians,  191 
of  Cyclostomata,  191 
diverticula,  193 
of  Dipnoeans,  191 
of  Teleosts,  191 
folds  of  mucosa.  193 
non-differentiated,  of  lower  verte- 
brates, 191 
folds  in  Amphibia,  196 
in  birds,  195 
in  fish,  196 
furrow,  primitive,  22 
glandular  apparatus   in   lower  verte- 
brates, 195 
groove,  primitive,  22 
juice,  function  of,  194 
mucous  membrane  of  Cervicnprn,  196 
of  Echelus  conger,  197 
Lophius,  197 
lymphoid  tissue.   196 
of  PhoccBna,  196 
of  Thalassochelys,  197 
rotation,  58 

arrest  of  development,  60 
demonstration  in  cat,  67 
spiral  fold,  function  of,  193 
vascular  supply,  63 

in  cases  of  non-rotation.  67 
villi  of  Carnivora.  195 
of  Casuarius.  195 
of  Ophidia,  195 
of  Ursus  maritimus,  195 
Intestine  in  early  human  embryo,  52 
general  consideration  of,  51 
large,  and  cfpca  of  Hyrax,  234 


I 


INDEX. 


287 


Intestine,  large,  functions  of,  198 

length  of,  199 

of  monkeys,  199 

of  rodents,  1,99 

width  of,  199 
small,  192 

absorbing  apparatus,  195 

divisions  of,  194 

length  of,  192 

secretory  apparatus,  194 

structure  of,  194 

villi,  195 
Isthmus,  duodeno-colic,  57 

TEJUNO-ILEUM,  development  of,  54 

T  ABRJJ^,  stomach  of,  44 
-"     Lagomys  pusillus,  colon  and  csecum 

of,  232 
Lagothrix   humboldtii,   ileo-colic   junction 

and  caecum  of,  215 
Lamellirostra,  ileo-colie  jiinction  and  caeca 

of,  203 
Lateral  vein  in  Selachian,  155 
Lemur  macaco,  ileo-colic  junction  and  cae- 
cum of,  213 
mongoz,  ileo-colic  junction  and  caecum 
of,  213 
Lemuroidea,  ileo-colic  junction  of,  213 
Lepua   cuniculus,    ileo-colic    junction   and 
caecum  of,  211 
saccus  lymphaticus  of,  211 
Lesser  curvature,  first  appearance  of,  41 
Ligament,  colico-lienale,  109 
of  ductus  venosus,  152 
gastro-lienale,  110 
lieno-renale,  109 
phrenico-lienale,  109 
Ligamenta  coli,  199 
Liver  in  Chelonians,  144 

comparative  anatomy  of,  144 
derivation  of,  34 
development  of,  141 
function  of,  195 
lobation  of,  144 
in  Ophidia,  144 

peritoneal   lines   of   reflection   in  em- 
bryo, 167 
in  foetus  at  term,  171 
peritoneal  relations  of,  167 
of  Petromyzon,  141 
unilobar  type,  144 
Lophius,  biliary  ducts  in,  145 

piscatorius,  mucosa  of  midgut,  197 
pyloric  appendices  in,  120 
stomach  of,  46 
Limgs,  derivation  of,  34 
Lutra,  biliary  ducts  in,  145 

stomach  of,  48 
Lymphoid  tissue  of  intestinal  mucosa,  196 

11TA.CACV8  cynomolgus,  ileo-colic  junc- 
■^"      tion  and  caecum  of,  214 
descending  mesocolon  of,  140 
lesser  omentum  of,  176 
mesosigmoidea  in,  140 
nemestrinus,  cheek-pouches  of,  48 
ochreatus,  ileocolic  junction  and  cae- 
cum of,  214 


Macacus,   peritoneum   of   infra-colic   com- 
partment, 136 
pileatus,    ileo-colic   junction   and   cae- 
cum of,  214 
relations  of   spleen  and  great  omen- 
tum, 139 
rhesus,  abdominal  viscera,  77 

ileo-colic  junction  and  caecum  of, 
214 
Mammalia,  ileo-colic  junction  of,  204 

pancreatic  ducts  in,  117 
Manatus    americanus,    ileo-colic    junction 
and  bifid  caecum  of,  208 
stomach  of,  48 
Mania   longicauda,   ileo-colie   junction   of, 

208 
Manidae,  colic  bend  of,  234 
Marsupalia,  ileo-colic  junction  of,  204 
types   of  ileo-colic   junction   and  cae- 
cum in,  218 
Meckel's  diverticulum,  35 

serous  folds  connected  with,  262, 
263 
Medullary  canal,  21 
groove,  21 
plates,  21 
Membrane,  cloacal,  24 
Mesenchyma,  30 

Mesenteric  peritoneum,  definition  of,  32 
Mesentery,  absorption  of,  33 
definition  of,  101 

jejuno-ileal,  line  of  attachment,  86 
of  umbilical  loop,  development  of,  56 
relation   to   adult  mesocolon 
and  mesentery,  72 
Mesoblast,  21 
Mesocola  in  cat,  86 
Mesocolic  fossa,  97 
Mesocolon,  ascending,  adhesion  of,  82 
in  monkeys,  83 

relation  of,  to  right  kidney,  83 
definition  of,  101 
descending,  adhesion  of,  82 
in  foetus,  83 

line  of  attachment  of,  83 
in  lower  mammals,  83 
in  Macacus,  140 
in  monkeys,  83 
transverse,  root  of,  85 
Mesoderm,  21 

derivatives  of,  28 
Mesoduodenum,  adhesion  of,  67 

definition  of,  101 
Mesorectum,  definition  of,  101 
Mesosigmoidea,  definition  of,  101 

in  Macacus,  140 
Mesothelium,  21 
Metanephros,  24 

Midas  geoffrei,  ileo-colic  junction  and  cae- 
cum of,  214 
ursulus,  ileo-colic  junction  and  csecum 
of,  214 
Midgut,  192 

extent  of,  38 
Monodon,  ileo-colic  junction  of,  209 
Monotremata,  ileo-colic  junction  of,  204 
Monotreme,  structure  of  penis,  26 
Monotremes,  biliary  ducts  in,  145 


288 


INDEX. 


Morphology,  general,  of  vertebrate  intes- 
tine, 190 
of  human  csecum  and  appendix,  237 
Morula,  20 

Moschus,  stomach  of,  49 
Muscular  stomach  of  birds,  50 
Musculocutaneous  vein  in  Anure  Amphib- 
ian, 158 
Mustela,  ileo-colic  junction  of,  212 
Mycetes    cobaya,    ileo-colic    junction    and 
caecum  of,  214 
fuscus,  ileo-csecal  folds  of,  264 

ileo-colic  junction  and  csecum  of, 
215 
Myoxus,  alimentary  canal  of,  211,  212 

stomach  of,  46 
Myrmecophaga  jubata,  ileo-colic  junction 

of,  207 
Myxinoids,  pancreas  in,  117 

'\TASUA  rufa,  duodenal  fold  of,  92 
-^V  ileo-colic  junction  of,  212 

pancreatico-gastric  folds  of,  181 
Necturus,  alimentary  canal  of,  40 

maculatus,  alimentary  tract  of,  52 
ileo-colic  junction  of,  201 
stomach  of,  43 
venous  system  of,  158 
Neuro-enteric  canal,  23 
Non-vascular  ileo-caecal  folds,  262 
Nucleolus,  19 
Nucleus,   19 
Nutritive  yolk,  19 

Nycticehus  tardigradus,  ileo-colic  junction 
and  csecum  of,  213 
spiral  colon  of,  234 
Nyctipithecus  commersonii,  ileo-colic  j\inc- 
tion  and  csecum  of,  214 

/TJ1S0PHAGEAL  gutter  of  ruminants,  49 
\Jjj     CEsophageo-gastric  junction,  45 
Omega  loop,  development  of,  77 
Omental  bursa,  107 

early  stages  of,  104 
Omentum,  great,  107 
layers  of,  107 

peritoneal  adhesions  in  adult,  131 
relation   of,  to  transverse  colon, 
transverse    colon    and    duoden- 
um,. 129 
lesser,    as    part    of   ventral    mesogas- 
trium,  165 
divisions  of,  172 
in  Macacus,  176 
Omnivora,  gastric  diverticula  of,  48 
Omphalo-mesenteric  arteries,  64,  146 

artery,  persistence  of  rudiments  of,  65 
duct,  22 
veins,  146 
Ophidia,  intestinal  villi  of,  195 
liver  in,  144 
stomach  of,  44,  46 
Oral  pouches,  48 

Ornithorhynchus  anatinus,  ileo-colic  junc- 
tion and  csecum  of.  204 
Orycteropus,    ileo-colic    junction    and    cae- 
cum of,  208 
Oryx  leucoryx,  ileocolic  junction  and  cse- 
cum of,  210 


Oryx  leucoryx,  spiral  colon  of,  233 
Otolicnus   crassicaudatus,    ileo-colic   junc- 
tion and  csecum  of,  213 
Ovis  aries,  spiral  colon  of,  233 
Ovum,  structure  of,  19 
Owl,  stomach  of,  50 

PANCREAS,  adhesion  of,  67 
adhesion    of    mesoduodenal    segment, 

123 
in  Ammocoetes,  117 
in  Chelydra,  117 
comparative  anatomy  of,  116 
concealed,  of  Teleosts,  117 
derivation  of,  34 

development  of,  in  Amphibia,  115 
of,  in  cat,  115 
of,  in  chick,  115 
of,  in  fish,  115 
of,  in  lower  vertebrates,  115 
of,  in  man.  111,  115 
of,  in  sheep,  115 
in  foetal  pig,  123 
function  of,  195 
in  Myxinoids,  117 
peritoneal  relations,  122 

vascular  and  visceral  relations  of 
adult,  125 
in  Protopterus,  117 
relation  to  dorsal  mesogastrium,  123 
to  mesoduodenum,   122 
to  omental  bursa,  123 
in  Selachians,  116 
Pancreatic  ducts  in  Mammalia,  117 
normal  arrangement,  113 
secondary,  111 
variations,  114 
Pancreatico-gastric  folds     in  man,  187 

in  Nasua  rufa,  181 
Papilla  Vateri,  114 
Paradoxurus  typus,  ileocolic  junction  of, 

212 
Paralichthys,  pyloric  appendices  in,  120 
Parietal  mesoderm,  21 

peritoneum,  definition  of,  32 
Pelamys,  pyloric  appendices  in,  120 
Pelvic  vein  in  Anure  Amphibian,  158 
Perameles  nasuta,  ileo-colic  junction  and 

csecum  of,  206 
Perca,  pyloric  appendices  in,  120 
Perennibranchiates,  stomach  of,  44,  46 
Perissodactyla,  ileo-colic  junction  of,  210 
Peritoneal  cavity,  lesser,  summary  and  de- 
velopment of  structure,  180 
relations    and    position    of    appendix, 
250 
of  appendix,  variations  of,  258 
sac,  lesser,  of  cat,  128 
Peritoneum,    arrangement    in    infra-colic 
compartment,  78 
of  cat,  compared  with  human  arrange- 
ment, 73 
of   infra-colic   compartment   in   adult 

human  subject,  88 
lesser  cavity  of,  in  relation  to  liver, 

174 
of  liver,  in  relation  to  lesser  sac,  174 
secondary  lines  of  reflection,  73 


INDEX. 


289 


Peritoneum    of    supra-colic    compartment, 

general  considerations,  99 
Petromyzon,  alimentary  canal  of,  200 
liver  ot,  141 

spiral  intestinal  valve  of,  119 
Peyer's  patches,  196 

Phascolarctos  cinereus,  ileo-colic  junction 
and  csecum  of,  205 
colic  loop  in,  234 
Phascolomys   wombat,   ileo-colic   junction, 

csecum  and  appendix  of,  206 
Pteropus  medius,  ileo-colic  junction  of,  212 
Phoca,  biliary  ducts  in,  145 

vituUna,   ileo-colic   junction    and   cse- 
eum  of,  212 
stomach  of,  45 
Phoccena  communis,  ileo-colic  junction  of, 
209 
intestinal  folds,  196 
Phylogeny  of  types  of  ileo-colic  junction 

and  caecum,  217 
Physeter,  ileo-colic  junction  of,  209 
Physiology  of  vertebrate  intestine,  190 
Pickerel,  pyloric  valve  of,  45 

stomach  of,  44 
Pinnipedia,  ileo-colic  junction  of,  212 
Pipa,  stomach  of,  46 
Piscivorous  divers,  caeca  of,  203 
Pithecia  satanas,   ileo-colic   jimction   and 

caecum  of,  215 
Placental  circulation,  146 
Placentalia,  definition  of,  36 
Plates,  medullary,  21,  28 
Platypus    anatinus,    male    genito-urinary 

tract  and  cloaca,  26 
Pleuronectes  m,aculatus,  ileo-colic  junction 
of,  201 
pyloric  appendices  in,  120 
Pleuro-peritoneal  cavity,  28 
Plicae  coli,  199 

Polypterus,  pyloric  appendix  in,  120 
Portal  circulation,  development  of,  147 

vein,  development  of,  148 
Position   and   peritoneal    relations   of   ap- 
pendix, 250 
Post-anal  gut,  23 
Post-cardinal  veins  in  Urodele  Amphibian, 

157 
Post-cava  in  Anure  Amphibian,  158 
in  Iguana,  159 
in  Urodele  Amphibian,  157 
Post-caval  vein,  151 
Pre-cava  in  Anure  Amphibian,  158 
Primates,  ileocolic  junction  of,  213 
types  of  ileo-caecal  folds  in,  265 
Primitive  aortae,  63 

common  dorsal  mesentery,  33 
dorsal  mesentery  after  rotation,  79 
mesentery,    effect   of   intestinal   rota- 
tion on,  59 
mesenteric  segment,  72 
mesocolic  segment,  72 
jugular  veins,  147 
Proboscidea,  ileo-colic  junction  of,  210 
Proctodaeum,  24,  26 

in  human  embryos,  27 
Protoplasm,  19 
Protopterus,  pancreas  in,  117 


19 


Proteus,  alimentary  canal  of,  40 

anguineus,  stomach  of,  43 
Proteles   lalandii,   ileo-colic   junction   and 

caecum  of,  212 
Proventriculus,  50 
Psalterium,  49  ^^^^^r      i"^ 

Pseudemys   elegans,   alimentary  canal  of, 
55 
ileo-colic  junction  and  caecum  of, 
201 
Pyloric  appendices,  119 
function  of,  221 
in  Accipenser,  120 
in  Oadus,  120 
in  Lophius,  120 
in  Paralichthys,  120 
in  Pelamys,  120 
in  Perca,  120 
in  Pleuronectes,  120 
in  Rhombus,  120 
in  Scomber,  120 
in  Thynnus,  120 
relation  to  pancreas,  121 
significance  of,  120 
appendix  in  Ammodytes,  120 
in  Echelus,  120 
in  Polypterus,  120 
caeca,  119 

fimction  of,  221 
stomach,  50 
valve,  44 

in  fishes,  45 
of  loon,  45 

T>  ANA,  alimentary  canal  of,  55 
■^     catesbia/na,  ileo-colic  junction  of,  201 

esculenta,  venous  system  of,  158 
Ratitae,    ileo-colic   junction    and    caeca    of, 

203 
Rectal  gland  of  Selachians,  201 
Rectangular  ileo-colic  junction,  225 
Recto-coccygeal  muscles,  33 
Recto-uterine  muscles,  33 
Rectum,  development  of,  54 

separation  from  genito-urinary  sinus, 
27 
Renal-portal   circulation  in   Urodele  Am- 
phibian, 156 
system  in  Selachian,  154 
in  Iguana,  159 
Reptilia,  abdominal  vein,  167 
biliary  ducts  in,  145 
ileo-colic  junction  of,  201 
Retro-gastric  peritoneal  space,  boundaries 
of,  175 
space,  rudimentary  form  of,  105 
Retro-peritoneal  hernia,  92 
Reticulum,  49 

Rhombus,  pyloric  appendices  in,  120 
Rodentia,  caecal  pouch  of,  229 
compound  stomach  of,  49 
ileocolic  junction  of,  211 
spiral  colic  valve  of,  231 
Rodents,  saccus  lymphaticus  of,  196 
Round  ligament  of  liver,  152 
Rumen,  49 
Ruminantia,  structure  of  stomach  in,  49 


290 


INDEX. 


SACCUS  lymphaticus  of  Lepus  cunicu- 
lus,  211 
of  Rodents,  196 
Salamandra  maculosa,  venous  system  of, 

158 
Salivary  glands,  derivation  of,  34 
Saurians,  stomach  of,  44,  46 
Sciatic  vein  in  Iguana,  160 
Scincus  ocellatus,  stomach  of,  45 
Scomber,  pyloric  appendices  in,  120 
Segmental  veins  in  Iguana,  160 
Segmentation,  20 
Segmentation-cavity,  20 
Selachian,  caudal  vein  in,  154 
digitiform  gland  of,  201 
duct  of  Cuvier,  155 
hepatic  portal  system  of,  155 
lateral  vein  of,  155 
pancreas  in,  116 
rectal  gland  of,  201 
renal  portal  system  of,  154 
spiral  intestinal  valve  in,  119 
venous  system,  154 
Semnopithecus,  stomach  of,  47 
Septum  urogenitale,  27 

transversum,  142 
Serous  folds  in  cases  of  Meckel's  divertic- 
ulum, 262,  263 
membrane,  derivation  of,  31 
Shape  of  caecum  and  origin  of  appendix, 
245 
of  embryonic  caecum,  245 
Sheep,  biliary  ducts  in,  145 

development  of  pancreas,  115 
Sigmoid  flexure,  development  of,  54,  77 
Simla  satyrus,  ileo-colic  junction  and  cae- 
cum of,  216 
Sinus  venosus,  146 
Sirenia,  ileo-colic  junction  of,  208 
Soft  palate,  42 
Somatic  mesoderm,  21 
Somatopleure,  22,  29 
Spigelian  lobe,  boundaries  of,  170 
development  of,  169 
recess  of  lesser  sac,  177 
Spiral  coil  of  colon,  233 

colic  valve  of  Rodentia,  231 
colon  of  Bos  indicus,  233 
of  Cervus  sika,  233 
of  Dasyprocta  agouti,  234 
development  of,  233 
of  Nycticehus  tardigradus,  234 
of  Oryx  leucoryx,  233 
of  Ovis  aries,  233 
fold  of  intestinal  mucous  membrane, 

function  of,  220 
intestinal  valve  in  Ceratodus,  119 
in  Cyclostomata,  119 
in  Dipnoeans,  119 
in  Petromyzon,  119 
valve  of  gastric  diverticulum  in  Bus, 
48 
Splanchnic  mesoderm,  21 
Splanchnopleure,  22,  29 
Spleen,  development  and  relation  to  dorsal 
mesogastrium,  108 
and  great  omentum  in  Macacus,  139 
pancreas  and  great  omentum  in  cat, 
127 


Spleen,  peritoneal  relations,  110 

vascular  connections,  108 
Splenic  artery,  65,  108 

flexure,  development  of,  54,  76 

vessels,  peritoneal  relations,  109 
Stomach  of  Alligator,  51 

assumption  of  special  functions  modi- 
fying form  of,  48 

of  Anguilla  anguilla,  47 

of  Batrachians,  44,  46 

of  Brady  pus,  51 

caecal  diverticula  of,  47 

of  Carnivora,  46,  47 

of  carnivore  birds,  50 

of  Castor,  46 

cellular  structures  connected  with,  47 

of  Cetaceans,  49 

changes    in   position   during   develop- 
ment, 102 

of  Chelonians,  45,  46 

of  Coluber  natrix,  44 

comparative  anatomy  of,  42 

of  Crocodiles,  46,  51 

of  the  Cyprini,  44 

definition  of,  as  segment  of  foregut, 
43 

embryonic  borders  and  surfaces,  41 

factors  modifying  form  of,  43 

first    differentiation    in    human    em- 
bryos, 40 

further    development    in    human    em- 
bryos, 40 

glandular,  of  birds,  46 

of  Oobius,  45 

of  Halmaturus,  47 

of  heron,  50 

of  Herbivora,  46,  47 

of  herbivorous  birds,  50 

influence  of  habitual  amount  of  food 
on  form  of,  44 
of  size  and  shape  of  abdominal 

cavity  on  form  of,  46 
of  volume  and  character  of  food 
on  form  of,  46 

of  Teleosts,  46,  47 

of  Labrus,  44 

of  Lophius,  46 

of  Lutra,  48 

of  Manatus  americamis,  48 

of  Moschus,  49 

masticating  surfaces  of,  48 

of  Myoxus,  46 

of  Necturus  maculatus.  43 

of  Ophidia,  44,  46 

of  owl,  50 

of  PerennibranchiatcR,  44,  46 

of  Phoca  vituUna.  45 

of  the  pickerels,  44 

of  Pipa,  46 

of  Proteus  anguineus,  43 

relation  to  vagus  nerve,  43 

ruminant  type  of.  43 

of  Saurians,  44,  46 

of  Scincus  ocellatus.  45 

of  Semnopithecus,  47 

storage  compartments  of,  48 

structural    modifications    of,    increas- 
insr  action  of  srastric  juice,  46 

of  Tamandua,  51 


INDEX. 


291 


Stomach,  transverse  position  of,  45 

type-form  of,  43 
Stomadaeum,  24 

in  human  embryos,  27 
Strix,  ca;ca  of,  203 

Structural  modifications  of  colon,  230 
Struthio  africanus,  ileo-colic  junction  and 

caeca  of,  204 
Sturgeon,  pyloric  valve  of,  45 
Subintestinal  veins,  147 
Submucosa,  derivation  of,  30 
Superior  mesenteric  artery,  64,  65 

relation  to  umbilical  loop,  66 
Suspensory     ligament     of     liver,     derived 

from  ventral  mesogastrium,  165 
8us  scrofa,  ileo-colic  junction  and  caecum 
of,  209 
spiral   valve   of   gastric   diverticulum 
in,  48 
Symmetrical    type    of    ileo-colic    junction, 
221 

T^NIA  coli-,  199 
Tamandua,  alimentary  tract  of,  56 
bivittata,  foramen  of  Winslow  in, 
183 
ileo-colic  junction  and  caeca 
of,  208 
stomach  of,  51 
Tapirus    americanus,    ileo-colic    junction 

and  caecum  of,  210 
Tarsius,  biliary  ducts  in,  145 

spectrum,  ileo-colic  junction  and  cae- 
cum of,  213 
Taxidea  americana,  ileo-colic  junction  of, 

212 
Tatusia    novemcincta,    ileo-colic    junction 

of,  207 
Teleosts,  anal  and  genito-urinary  orifices 
in,  25 
concealed  pancreas  of,  117 
development  of  liver  in,  143 
gastric  diverticula  of,  47 
intestinal  canal  of,  191 
stomach  of,  46,  47 
without  pyloric  appendices,   120 
Thalassochelys,  intestinal   folds   of,   197 
Thymus,  derivation  of,  34 
Thynnus,  pyloric  appendices  in,  120 
Thyroid,  derivation  of,  34 
Tolypeutes,  ileo-colic  junction  of,  207 
Transverse  anal  fissure,  27 

colon,  development  of,  54,  244 

differentiation  of,  76 
mesocolon,  development  of,  80 
Trichosurus    vulpinus,    ileo-colic    junction 

and  caecum  of.  205 
Trigla,  biliary  ducts  in,  145 
Troglodytes  niqer,  ileo-colic  junction  and 

caecum  of,  217 
Types  of  ileo-caeeal  folds  in  Primates,  265 
ileocolic  junction  and  caecum,  phylo- 
geny  of,  217 

UMBILICAL  arteries,  63 
hernia  of  embryo,  52 
loop,    derivation    of    adult    intestinal 
segments  from,  53 
divisions  of,  52 


Umbilical  loop  of  embryonic  intestine,  52 
relation  of  vitello-intestinal  duct 
to,  52 
veins,  147 

changes  after  bfrth  in,  152 
final  arrangement,   151 
further  changes  in,  149 
intra-hepatic   distribution,    152 
vesicle,  22 
Umbilicus,  21 

Ungulata,  caecal  pouch  of,  229 
ileocolic  junction  of,  209 
Urinary  bladder,  in  human  embryos,  27 

relation  to  allantois,  24 
Urinator  imher,  diverticulum  caecum  vitelli, 
35 
lumme,  diverticulum  caecum  vitelli,  35 
pyloric  valve  of,  45 
Urodaeum,  25 

Urodele    Amphibian,    abdominal    vein    in, 
157 
caudal  vein  in,  156 
ducts  of  Cuvier  in,  156 
hepatic-portal  system  of,  157 
iliac  vein  in,  157 
post-cardinal  veins  in,  157 
post-cava  in,  157 
renal-portal  system  in,  156 
venous  system  of,  156 
Uro-genital  cleft,  27 
Ursus,  ileo-colic  junction  of,  212 

maritimus,  intestinal  villi,  195 
Uvula,  42 

VAGUS,  gastric  distribution  of,  43 
"Valves  of  Kerkring,  196,  197 
Valvulae  conniventes,  196,  197 
Variations  of  caecum  and  appendix,  244 
in  the  peritoneal  relations  of  the  ap- 
pendix, 258 
Vasa  intestini  tenuis,  66 
Vascular    mesenteric    folds    of    ileo-colic 
junction,  262 
system  of  liver,  development  of,  145 
Vein,  portal,  development  of,  148 
Veins,  anterior  cardinal,  147 
hepatic,  148 

omphalo-mesenteric,  146 
posterior  cardinal,  147 
primitive  jugular,  147 
subintestinal,  147 
umbilical,  147 
vitelline,  146 
hepaticae  advehentes,  147 
revehentes,   147 
Venous  system  in  Anure  Amphibian,  158 
of  bird,  161 

of  human  foetus  at  term,  162 
of  Necturus  maculatus,  158 
of  Rana  esculenta,  158 
in  Selachian,  154 
of  Salamandra  maculosa,  158 
of  Urodele  Amphibian,  156 
Ventral    mesentery,    early    condition    and 
derivation,  31 
mesogastrium,  163 

in  Iguana,  166  * 

and  liver,  140 

relation  to  duodenum,  164 


292 


INDEX. 


Ventral   mesogastrium,   relation  to  liver, 
105 
to  umbilical  vein,  165 
vascular  ileo-caecal  fold,  262 
Vertebrate   intestine,   general   morphology 

and  physiology,  190 
Visceral  mesoderm,  21 

peritoneum,  definition  of,  32 
Vitelline  arteries,  64,  146 
membrane,  19 
sac,  20 
veins,  146 

anastomosis  of,  147 
Vitello-intestinal  duct,  22 
Vitellus,  19 

Vulpes  fulvus,  ileo-colic  junction  and  cae- 
cum of,  212 


W 


ATER-CELLS  of  camel's  stomach,  49 
Wolffian  duct,  relation  to  primitive 
intestine,  24 


l^ENURUS,  ileocolic  junction  of,  207 
-^      Xiphias,  biliary  ducts  in,  145 


YOLK,  19 
Yolk-sac,  20 


^  AL0PHU8   gillespiei,    ileo-colic   jxmc- 
^      tion  and  caecum  of,  212 
Zona  pellucida,  19 


1 

DATE    DUE    SLIP 

UNIVERSITY  OF  CALIFORNIA  MEDICAL  SCHOOL  LIBRARY 

THIS   BOOK   IS   DUE    ON    THE   LAST    DATE 

STAMPED  BELOW 

1 
14   DAY 

aUL  31W4 
OCT  25  1924 

JUN  2  2  1979 
RCTUHNEO 

DCC    3  1924 

JUNm»!St 

NOV  2  11925, 

DLG  iiJ^  i925i 

1927 

APR  1  0  1929 

^£C  1 8  1929 

MG  2  i  1933 

■"    1 

HOy  4     193^ 

1 

FEB  11  1937 

* 

27n-8,'23 

V. 


QM567      Hiintington.   JG.3.    c424 
H95  The   anfetoirfy  of  the 

1903  human  peritoneum 


opment  ... 


and  abdominal  cavity 
considered  from  the 


standpoint  of  devel» 


3424 


Library  of  the 


